The buttons do different things depending on what you are doing. At the front is a trigger. It is usually used for taking actions like pressing things, selecting things, pulling triggers, etc. The middle trigger (you grab it with your middle finger) is typically used for grasping things. Then you have two raised buttons on each controller. On you right hand you have A & B on your left hand you have X & Y. This is the same thing as on a traditional Xbox controller. Again they do different things depending on the game. On each controller is also a non-raised button called the oculus button or menu button. Quick pressing the right menu button brings up the menu. Long pressing the right menu button re-centers you. The left menu button does nothing in the oculus home, but it usually brings up the game's menu. So, you just have to learn how each game uses the buttons. Most games will give you a tutorial to let you know what each does. Only the right menu button stays the same no matter what you are doing. Hope this helps.
Also make sure you do the two demo apps. First steps and Oculus first contact.
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