I registered with sitcomsonline.com and i have no clue on how to sign in and out when i leave the site and when i go on the site. Could someone please help me with this problem?

Why do you need to sign out? Are you on a school or library computer? There's a Log Out link on the bottom of the main message board page.

If it's your own computer, then it is designed to remember your username and password so you don't have to login every time.