1. Head over to steem-engine and log in with either the keychain or steemconnect.
2. Make a purchase of the AAA tokens (if you have not).
3. After you are sure the trade is complete/tokens are available in your wallet, click the wallet tab (this step helps you to view all your token balances),
4. and on the raw AAA is stated, watch the right end where a padlock icon is situated (hovering over it makes a pop up of Stake),
5. enter amount to stake (not more than what you have) and proceed with the confirmation which will also happen over steemconnect log in.

Confirm the transaction is complete and there you have your AAA staked.