Games can be added by manually creating folders and the .ini file. However, I recommend using the Entry Helper button located under the Config section.
The Entry Helper allows you to see which fields need to be filled in for a given game. Essentially, this is an editor for the game's .ini file.
If starting a new game, I would recommend creating the games folder and then, within the Entry Help screen, fill in the ini file with the name of the game or a nickname for the game. Then use the "Create Default Folders and Ini File" button located in the Entry Helper screen. This allows you to then browse to directory you want to use for the game and automatically creates the .ini file and all the sub-folders used by MEAGRE.