Please watch the Steem basics video posted above between the 1:21 and 2:21 minutes duration. Here you will be taught to go to the exact location of the keys and the names of the keys and their special uses.
IF YOU GO THERE, YOU WILL FIND THE LIST OF POSTING KEY, ACTIVE KEY, OWNER KEY AND MEMO KEY.
TO PERFORM THE WALLET-RELATED OPERATIONS, YOU NEED TO USE THE "ACTIVE KEY," WHICH IS ALLOTTED FOR YOUR ACCOUNT.
Hope this clarifies your doubt.
RE: Important Changes to Steemit.com and Wallet