1. Close Maya
2. Unzip Folder
   The first thing to do, and it might sound a bit obvious, is to unzip the file you just got.
3. Copy Files
   Place the “cosmos” folder in Maya’s script directory. Normally it’s here:
   Windows Vista and Windows 7
   \Users\<username>\Documents\maya\scripts
   Mac OS X
   ~<username>/Library/Preferences/Autodesk/maya/scriptsLinux (64-bit)
   ~<username>/maya/scripts
   
   If you have issues finding the script folder, run the following command in Maya as mel:
   internalVar -userScriptDir
   
4. Add startup-command
   Add the following line to your userSetup.py in the “scripts” directory:
   import cosmos
   (If it doesn’t exist, use the one from the unzipped folder, or create a new blank text file with the above text)
5. You are ready to roll!
   Next time you start Maya you should be able to activate Cosmos with the shortcut:
   

    

   Windows	CTRL + TAB
   Linux	CTRL + TAB
   Mac	SHIFT + TAB

Ps. You can, of course, add Cosmos to whatever shortcut you want with the following code in the hotkey editor:
cosmos.start()

If you still have questions, email me and I help you get it up and running 🙂