Here is a Power Play guide:
PP Guide
Basically, within the Federation, the Achenar Empire, the Alliance of Independent Planets and the true Independents there are individuals. Movers and Shakers. 10 of them. Each looking to increase their influence over the galaxy. There are 4 in the Empire, 2 Feds, 1 Alliance, and 3 Independents. YOu pledge your support to one if them and perform activities on their behalf. These give you merits to hand in to improve your Rank within their organization. For the Big 10 its all about Real Estate. Star Systems generate income called Command Capital (CC) but they also cost CC to maintain. A CONTROL system generates this CC from every system within 15 LYs of it, these are EXPLOITED systems. The exact amount of CC depends on the stuff in the systems as well as the individual governments in each of those systems. A good system generates more CC than it cost to maintain. There are the systems you own or CONTROL. The idea is for all your CONTROL systems to generate extra CC. This will allow you to target new system you want to bring under your control. You start PREPARING these systems. Multiple powers can prepare the same system. Who ever does the most preparation at the end of the cycle (a cycle is 7 days Thurs-Thurs) can then try to EXPAND into that system next cycle. If you successfully expand you now control that system and add it to your CC generation/costs. And the cycle begins anew.
Each Power Player has a Reddit and Forum community. Some are better than others. Here real players try to coordinate the efforts of the group for the best results (in theory).
There is a strong Role Play element by pledging support to this or that Power. Not to mention that other PP players and NPC are now flagged as enemies and may attack you.
There is a fair amount of combat but some PPs use it more than others to Expand and Undermine. Pick your Power carefully if you are looking for combat. <cough.cough.Archon Delaine>
Good money can be generated in PP. Since you spend a lot of time working for your Power Player its only fair they pay you a little bit. Its fairly easy to earn enough merits to hit and maintain RANK 4 which pays 5 Mil each week. With some dedication you can hit and maintain RANK 5 which pays 50 millions per week. At least it does for Archon, I think all the Powers are the same but I'm not sure. There are also other perks detailed in the guide for each Power.
I hope all that helps