To automatical game downloading and launching you may use instead-launcher. If you do not want to use it, you may download and install games manually.
To launch game you must download INSTEAD first. Just press red Download button in top-right corner.
To install game you must unpack zip archive with game in INSTEAD games directory. For windows users this directory is inside INSTEAD application directory.
For Unix systems you may unpack game in ~/.instead/games.
You also can install .zip file right from running INSTEAD. Go to menu, select game and press «…» button. Then select .zip file and press open.
Some games can be found here.
Unofficial games repository
Here are a lot of games from Unofficial repository. You may look on screenshots by pressing on they titles.