Wallet
What is the wallet?
The wallet is a Solana wallet. It has an address, secret key and a balance.
Address
The address is exactly as it sounds, it's your wallet's address! Same as your house address it uniquely identifies your wallet and is a publicly available piece of information. If someone ever wants to send you any SOL (the currency of Solana) they can send it your address.
Secret Key
NEVER. EVER. NEVER. EVER. Tell anybody your secret key. Your entire wallet will be compromised and you will just have to let it go. Don't be an idiot. NEVER EVER GIVE ANYBODY YOUR SECRET
With that warning out of the way... Your secret key is basically the password to the wallet. You can use this in apps like Phantom to open and interact with the wallet in more advanced ways than just in the Don't Die App.
Balance
How much money you have! The balance is how much SOL you have in your wallet.