Cisco IOS Router Basic Configuration

Thank you Rene I understand the concept of “login” and “login local” but my question about password encryption let me explain to you my question in another way:
login local refers to a local database on the router or switch with usernames / passwords as you said but the password possible to be encrypted or not if I configure it in plain text how can I change it to encrypted Text or vice versa ,
this is my question?

*when I try to change it this message appears to me :

SW3(config)#us hussein pa 121212
ERROR: Can not have both a user password and a user secret.
Please choose one or the other.

how can I change between them?