How do I exit the wallet and get back to the app?

Tap the back arrow at the top left. It takes you back to where you were.

Phone app

The Wallet has its own bar at the bottom (Home, Buy, History). The back arrow at the top left, or your phone's back gesture, takes you out of the Wallet.

Desktop app, Website

Click any item in the menu on the left to leave the Wallet, or use your browser's back button.