You can do both! its under your settings

It would more than likley be something called security settings.

Your current passward it eather the last 4 ditgits of your phone number or 0000

a phone lock is just in case you leave your phone somewhere so that other people wont go through your stuff...like your parents

so nobody can access your information besides u or a person who knows the code

YES. JUS GO TO "LOCK PHONE ON POWER-UP"