Download GameJolt API for CF2.5 or MMF2: http://gamejolt.com/games/arcade/fusion-2-5-gamejoltapi/27301/
You can try it out by running the .exe
To open and use the .mfa you need:
Full version of Clickteam Fusion 2.5
Get Object (http://www.aquadasoft.com/Get.zip)
String Tokenizer (http://www.aquadasoft.com/StringTokenizer.zip)
String Parser (http://www.clickteam.com/webftp/files/mmf2/Exts/MMF2ExtPack1.exe)
xLua (http://taloncrossing.com/xlua/xlua-dist.zip)
Unpack the contents (except the .exe) and put all the files in the Fusion directory, then restart your Fusion
To make your games have the API, simply put all the objects outside the frame into your application. Then copy and paste the GameJolt API group found in the events editor.
Use the examples to use the API.
You will need to use the INI++ in order to get info from the achievement system.
I will probably do a video tutorial if I have time. But for now I hope that this is not as confusing as it was before.