There are a number of options to specify your satellites drag and SRP properties in STK but sometimes you just need more detail than the default settings allow. Drag plugins allow you to customize pretty much any parameter where the GUI does not give you the detailed capabilities you may need.
Take a look at the sample drag and SRP plugins FAQ to get you started. This also contains instructions for registering the plugins. The DragSrpAreaFromAngles example assumes you have a typical box shaped satellite with one face aligned with the velocity vector. The solar panels stick out the side and are pointed towards the Sun, similar to the image below.
So you end up with a drag area that’s a constant value (due to the satellites body) and a sinusoidal component due to the rotating solar panels.
You also have the option to align your solar panels with the velocity vector while in umbra to decrease drag.
The plugin pulls the direction of the velocity and Sun vectors from STK, performs a few projections and dot products, and determines the current drag and SRP area. These areas are then pushed back into STK and the propagator (HPOP or Astrogator) will then use these custom values