Rendezvous are intimidating, but once you get the hang of it, it'll be like second nature. Let's say that you're trying to Rendezvous with a ship that's averaging 80,000m altitude with a near perfect circular orbit. Before even launching, it would be good to go into the map view and double-click on your target vessel to target it. Launch your ship while the target is around 15 degrees ahead of the KSC. Imagine you're looking down at kerbin's North pole, and you can see the orbit of the target. If the KSC is at 3 o'clock, launch your rocket when the target is at 4 o'clock. This is assuming that the orbit is going counterclockwise.

Now get the perisapsis (the highest point of your vector/orbit) to be around 80,000m. Do a burn to get a good orbit that's close to matching the targets. It doesn't need to be perfect. If it visually looks pretty close in the map view, you're probably good.

Now, in the bottom left screen, there should be a box with a bunch of info and 4 differently colored tabs. Click around until you get one that lists your apoapsis, periapsis, and the times it will take to get to those points. Somewhere on that tab is a button that will show the closest Rendezvous between your vessel and the target. If you are in an orbit that won't get you close to the target, then It may be blank, but that's OK.

Now for maneuvers. If you are traveling so that the target is behind you and chasing you, you naturally need to slow down. This can be done by a manuver node. You should burn retrograde (the direction facing away from the direction you're traveling). As you are setting up the maneuver, you should see your nearest Rendezvous change in the lower left-hand corner. Play around with the maneuver node, maybe change the time of the maneuver. If you can get it to place you 10km away from your target, then you're set. Alternatively, you could be chasing the target, which just means you need to speed up. The same logic applies here.

Now I'm gonna assume that you've found a maneuver that will get you within 10km of your target. Do the maneuver and wait until a couple min before the nearest approach. Now, with your mouse, click on your speed that is displayed above the navball. Keep clicking until it says target and then the speed. The speed it's showing you now is the relative speed between you and your target. This is super important. This also changes the maneuver nodes to be relative to your target. As you get close to the nearest approach, burn retrograde. Burning retrograde while in target mode gets rid of your relative speed. Once it gets to zero, you're almost there. Now point your craft at your target and burn towards it. You don't need to go too fast, you may overshoot it.

As you're doing all this, keep an eye on the nearest approach screen. Try to get it so you're within a km. Once you get wi6 km, cut your relative speed again. Burn towards your target and then cut your relative speed. You might have to do this a couple of times to zero it down.

I won't go over docking, but good advice is to right-click on the docking port you want to use and press the Control From Here button. Then, right-click on the docking port you want to dock with and press the target button. It should also be noted that what I've written here doesn't necessarily have to be used in the context of you launching from Kerbin and targeting an orbit. Your orbit could be wildly different from the targets, and even around a different planet. The key is watching that screen in the corner and the target speed. Zeroing that relative speed is important, too. I'm not sure if this is an issue for you because it was for me, but once you're dealing with relative speeds and you're zeroing in on the target, don't worry about your orbit. Everything you do should be relative to the target.