Prior to installation, have Sins of a Solar Empire: Rebellion (SoaSE:R for future reference) installed. If you have played Sins of the Prophets before, delete any previous copies of the mod from your Sins mod directory first. Launch Sins of a Solar Empire: Rebellion - From the Main Menu, go into Options, mods, and click show mod path; this will create a folder within the SoaSE:R mod directory, allowing for proper installation of mods. Extract the folder in the zip file called "SotP Alpha v.0.81.2" to your Sins mod directory. If your SotP mod folder contains the readme (this document), you've extracted the parent folder of the mod into SoaSE:R's mod folder, and you'll need to pull the further SotP Alpha v0.81.2 mod folder out of it in order for the mod to work. It cannot be nested in extra folders for SoaSE:R to pick it up properly.