How does Frosty Mod Manager for MEA work?

There are two parts of the Frosty tool suite:
The Editor, used to create new mods
and the Mod Manager used to apply mods and play the game with them.

For both of those holds true:
Unpack them (preferably in a location that is not C:/Program, or C:/ProgramFiles (x86), IIRC Desktop is also a bad place).
Set them up in the ignore list of firewall(s), antivirus software and similar.
Start the exe and point it to the correct game-executable.

For the mod manager:
import the zipped mods you want to play with. You also need to 'apply' them in the current profile. There can be several profiles, but only mods applied to an profile are loaded when you start the game with that profile active.
Always start the game through the mod manager when you want to play with mods enabled. Starting the game through origin or other means will not apply the mods.