If you want the two blogs to be completely separate from each other you can set up a new account with a different email address and different password.
But you can also set up another (or more) blogs on your current account and use one password to log into them. After you log in you'll see a list of the blogs connected to that account when you hover over your gravatar on your administration bar on the top right. Choose the one you want to edit.
For example I have two blogs using my work email, and several blogs using my personal email. For practical reasons I wanted them completely independent of each other.