Save it to any where on your computer, perferably "My Documents" once it is downloaded, go to my documents and extract the files using IZArc (Free rar/zip opener) and "Extract the files" once you done that open the folder and read all of the files in it, especially the ones in the documentation folder.

Galaxy forge -> Just open it

Particle forge, developer.exe (any version) -> copy and paste contents of the folder into Program Files -> Stardock Games -> Sins of a solar empire or where you saved the main install directory

You might need to download the newer version of the developer.exe for the latest patches.

Note; also the game info (reference data) files within the forge tools are for 1.15 and 1.01, and if you are fully updated to 1.17 and 1.03 won't work. You will need to get a convertdata GUI to make a new gameinfo(reference data) from the games folder.