You need to have an Ambire Wallet account as well as $WALLET tokens in it, which you can stake. There are few ways in which you can get $WALLET tokens, which you can find in this article.
Furthermore, you need to have some funds to pay the gas fee, or use the Gas Tank option to pay the fees for the transaction.
You do not need to be online or have your wallet connected at all times to earn rewards. You will be earning rewards regardless if you are online for as long as you have an active stake.