The main point is that none of it really matters. Wherever you are, if you do stuff for the station, like kill their pirates, sell stuff to the, do their missions, give them data, etc, they'll start to like you and give you better missions. That's how you make bucket loads of cash from doing certain types of missions in certain places, like Robigo passenger missions, Ngalinn pirate massacre missions and Cubeo mining missions.
You need high Federation rank to get the Corvette and high Empire rank to get the Cutter. Those military ranks increase a bit each time you complete a mission for any faction that has the Empire or Federation symbol next to them. All factions are one of Empire, Federation or independent. Empire and Federation are called superpowers. There's another weird rank with the superpowers that goes up and down, but doesn't mean anything, except you have to get one temporarily high to unlock an engineer. It's basically how much they like you. When you work for them, it goes up, and when you rest, it goes back down. You mustn't confuse it with the military ranks, which only go up.
When you do stuff for anybody, it has no negative effect for you, with one exception. If you fight in a a conflict zone against the main faction, your ranking with them will eventually turn to "hostile". That will make the station turn red and you'll get blown up if you come to close to it.
If you fail to complete any mission for a faction after accepting it, your rank with them will go down.
In summary, there are ranks withe each faction, ranks with the superpowers, and Powerplay ranks, as well as your own ranks for trade, combat and exploration. You can even sign up to Inara and get a load more ranks for all sorts of things. You can influence which faction and superpower controls a station by doing stuff for them. Powerplay is separate, and it's about which politician controls what area of space. You don't need to worry about doing anything for the wrong side, except fighting in a CZ. When you kill pirates, everybody loves you except the pirates, but even they don't bear any grudges.
