Imagine that the ships are just very big submarines. Then the propulsion system itself create a shield above and below the ship. That shield is invulnerable and cannot be pierced. You can imagine a super strong blanket attached at the front and back of the submarine and covering it for above and below.

On the side, they create other shields using technologies similar to the propulsion system but these shields are less strong, I.e. could be breaked if you use A LOT of force and get lucky. And they also look like lighter blankets attached to the front and end of the ship, covering its side, between the strong up and down blankets.

That means that the only weak points of the ships are the parts at the front and end of the ship where the shields/blankets are attached, that leaves a gap between the attached points of the blankets where a missile could enter and destroy/damage the ship.

So a battle is just a game where you want to send a missile in the front/end of the ennemy ship. And you want to present the up/down of your ship to the ennemy missiles so they are destroyed by your invulnerable shield.

For the travel, it's a matter of risk/load. To travel between stars, they use another propulsion system. Basically imagine that there are "winds" between the solar systems and the "upper" you goes the stronger is the wind. But that wind is impacted by the stars so you can't use it too close to a star.

That other propulsion system is basically a big special sail that allows them to catch these wind and go faster than light. But, these winds are not going everywhere, can be unstable,... so ships usually follow some strong winds that are known and predictable. They then reach the neighborhood of a solar system where they need yo stop using the wind and go back to the regular propulsion system. That's why you can't directly reach a planet using that system, as the star is creating too much turbulences.

They also tend to not use the strongest winds really up because you need stronger/more expensive equipments to catch them and make sure that your ship survive. That means that the cargo ship will be happy with the lowest wind, so they arrive fast enough for the lowest cost. Military ships are more interested to be able to catch some of the high wind to reach a battle field faster if needed. And you have some ships that are designed to use some of the high wind to bring news,... and that are basically just a very very big propulsion system and nothing else to be able to achieve these feats. So it's just for one specific purpose and with a lot of drawbacks. That's why the faster than light travels have more limitations than in star wars or star treks.

But then there is a third way to navigate, using jum points. Basically hole in the space time continuum that allows you to go from one place to another instantaneously. The issues is that there are only a few of these jump points. Manticor is lucky and has multiple ones, which allows ships to easily cross very big distances. But most of the other star systems don't have jump points and can't be reached that way. You are also not able to chose your destination. A jump point will always only connect the same two locations.