The grip buttons are used for moving around via teleportation. Push it down and point at the location you want to teleport to. A green beam means you can move there, whereas red means you need to choose another location.
Trackpad movement is, for many, a more natural and immersive way to play virtual reality games. It can make players slightly queasy if they're new to it, however.
To move using the trackpad, aim your Vive controller in the direction you wish to travel then press the trackpad down also in the direction you wish to travel.
If you find that you're moving too slowly, press the trackpad down on both Vive controllers to run.
Use the Trigger button for picking up and dropping items. Squeeze the Trigger once to pick an item up. The item will attach to your hand. Squeeze the Trigger again to drop the item. There's no need to press the Trigger the entire time you're holding an item!