To add a game to your favorite list, click on the "Heart" symbol at the bottom left of the game tile.

 Figure1: Three games are marked favorite

You can easily find your favorite games by clicking on the "Favorites" tab beside the "All Games" tab in the Lobby.

 Figure 2: View from the Favorite Tab

You can remove a game from your favorite list by clicking on the "Heart" symbol on the game tile again.