Steemit has a master passwords, and you should not lose control over it in any given moment. So, once when you have it, save it in safe place, the best on some offline media.
But the problem is that there are a few passwords in the Steemit and an each has a different purpose.
The first and the only rule, do not paste your master password in anything that you do not understand.
For anything that uses STEEM outside of main page or Steemit, it is enough to use either the ACTIVE (used to make transfers and place orders in the internal market) or POSTING (posting and voting) key.
Besides the OWNER key ( that is a master password) there is another one called MEMO that is used to create and read memos.
There are many apps that will ask you to use any of these keys, one of them is so called login application Steem Connect that servers as a bridge between Steemit and smart applications based on STEEM ( all those other pages you can use, front ends, programs …)