If you use the master password you were given at the start I urge you to stop using that. It's the most important password you have and you should never ever use it. Make sure you back it up properly.

For daily activities on steemit use your posting key to login. You can find it under wallet --> Permissions ---[show private key].

Login with that key and your username for daily activities.

If you want to transfer funds use your active key (in the same screen).

Again make sure you backup your MASTERKEY properly.

To store passwords you can use a password manager like, Lastpass or 1password.