Sign-In Confusion

I'm new to this. So, I apologize in advance if this questions causes eye to roll! I downloaded Digital Editions on one of my computers yesterday. After doing this, I created my profile (ID/password) and uploaded a few books. Later, I downloaded Digital Editions to a second machine and want to view the books I uploaded earlier. However, I can't figure out how to sign in so that I can see them. Any help would be appreciated.