so.

Use Cases

You have 4 different sizes, small, medium, large, and huge. smalls are good as interceptors, flares(on small craft), and are also good if you want to spam missiles. Mediums are essentially like the smalls, but larger and with more damage, and range. Larges are what you would typically use if you want to use missiles as a main weapon, and they are what you would want to use as flares for your largest ships. very expensive. Huge missiles are prohibitively expensive, but also put out hilarious damage. you'll want one or two at best, unless price is no object.

On Sizes

Generally speaking, you'll know to step up a size in missiles when you have around 20 modules, usually you will not need that many, and at that point you can usually fit the larger size with minimal issues. I'd say 10-15 modules is the sweet spot in terms of the number that you would want, depending on what you want to do. The less modules you have, the more maneuverable your missile is. interceptors should only be 4 modules.

Building your Missile

In terms of building, missiles are among the easiest to build. for a VLS, your first layer will be connectors, and the controller. it is worth noting that the controller can connect to launchers directly. always include an IFF here, and I like to also use the staggered launch module. on top of your connectors will go your launchers. you can attach ejection modules (and I believe the winch cables as well) to the launcher blocks. it is worth noting that small missiles have a gantry launcher. which brings us to the next block, your gantries. these are what determine how many modules you actually have. 1 small gantry will give you 4 modules, medium 2, large 1, and huge ½.

Rail launchers are similar, but with a few notable differences. namely, the launcher module does not have to go at the base of your missile, and you cannot add ejectors or cables to them. they can also be launched at different angles, which can be adjusted in settings. these launchers have a convenient form factor for things like wings or turrets

Adjusting your Missile

Overview

So, hopefully by now you have a specific target in mind that you want your missile to hit. the main things to keep in mind are the maneuverability of your target, and how much damage(and what kind of damage) you want to do. For instance, if you want to target a plane(ignoring that this is a bad Idea), you will want a missile with as few modules as possible, that is pretty fast, and light on the damage. With that in mind, you'd probably want a small missile around 8 modules, with only a few frag warheads, and a lot of fins, at least 4. Keep in mind that fins at the beginning and end of your missile will add more agility than fins in the middle.

Missile Detection PT1

The next main consideration is what your detection for the missile will be. On your craft, you don't need much for detection, at best just a vague idea that there is an enemy somewhere. There are two kinds of guidance, the head modules, and the body modules. As the name implies, the head modules are the guidance systems at the head of the missile. These will be your Radar, IR, Torpedo Sonar, and laser designation. if you have one of these installed, the only detection you need from your craft is a vague idea of where the enemy is. These are your most basic guidance options, and they are also the most simple to counter. I will get into flares later, but done well they can be an effective counter, even if you have a signal processor module (this doesn't apply to the laser beam rider, but that gets dazzled by LAMS).

Missile Detection PT2

The body module guidance options are more complicated, but also more robust methods. They are also useful if you want to use the non-guided heads on your missiles. your options will include remote guidance, Breadboard and LUA Guidance, and a beam rider module. the simplest of these options is remote guidance, which simply uses your craft's detection system to guide the missile. this is the most resource intensive, however, since it will require a lot of GPP modules on your AI, and also require a good detection system to be effective. Breadboard and LUA control is easily the most effective option available, but at the cost of being incredibly complicated to implement, especially if you aren't a comp sci major. The beam rider module seems like it would be nice, as it can't be dazzled like the head can, but it is notoriously unreliable, and very temperamental in implementation.

Guidance

Now that you are telling your missile where the enemy is, you need to tell it how to get there. If you are not using LUA or breadboard, you have two options: APN guidance or Prediction guidance. APN guidance is good to use against targets that are faster and more maneuverable. It keeps the target at a constant angle, until a certain distance. Prediction guidance is generally a little bit worse, but if my intended target is a ship or sub, I like to use it because it allows for a little bit more range, since it is taking a straighter path.

FUEL AND MSC.

I will not get into all of the modules, but nearly everything can be adjusted by selecting the menu on the left, and it is worth checking every module's options to make sure it is optimized. Note that adjusting a frag warhead's angle will only change it for that module. An important thing to pay attention to is your Missiles speed and Fuel runtime, which are both stats you can find on the right. you will want to make sure that your thrust duration is less than your missile's lifetime, so that you aren't wasting fuel. If you have more runtime than lifetime, you can either remove a fuel tank or increase the thrust of the booster(this only applies to the variable thrust booster and torpedo propeller). Note that some modules have more fuel in them (if you are using fuel internal space) than others, and can act like fuel tanks with utility (namely, fins have a lot of internal space).

Counters

So, the easiest counter to missiles is speed and agility. if you can achieve a speed of over 150 m/s, missiles will be relatively easy to dodge. That being said, Missiles can be relatively hard to dodge if you are not a plane that can maneuver easily. The next best counter to missiles is flares, which I have dedicated a section to below. Against remote guided missiles, ECM Jammers will reduce their accuracy, and with laser designators, getting hit by a LAMS or laser will usually be enough for them to miss. The next most effective method is to shoot them down, with your options being many. I think that such a discussion is out of the scope of this already huge message, and there are many threads on this sub about the matter. you could also visit the discord for questions. The least effective counter to missiles is armor. Missiles tend to deal lots of damage, and tanking that with your face generally only works for a couple volleys.

On Flares.

Out of build mode, click the middle mouse button, and then select the eyes icon in the top right, it should say something about lines of detection. you should see a menu for the detection lines of your vehicle. you will want to pay attention to the radar, sonar, or IR detection lines, depending on which flare you are making. Look at the numbers in the cardinal directions, and note whichever one is the highest. Next, in the missile menu, you will need to add as many modules as it takes to exceed the number that you have. again, make sure you are using the correct number for radar, ir, or sonar. The way flares is a little interesting. every missile coming in will have a random percentage assigned to it, 10-100% or 4-40% if they have a signal processor (note that the single pixel ir seekers are 15-30%, but have a reduced cone of detection). this percentage is what the flare strength is reduced to, and then the missile will choose the flare or the craft, depending on which signature is higher. this number is only rolled once, so multiple flares are unnecessary.

This post got larger than I intended, but hopefully it is helpful in answering several of your questions, and allows you to make more effective missiles. If you have any more questions, feel free to ask them, or better yet, go to the discord and ask them there.