When login, if you don't select "remember my
login", your session will expire when you close
your browser.

If you select "remember my login", the session
won't expire even if you close your browser
so you won't have to login again when you come
back to the site...

Currently, there isn't any "logout" button :
If you choose to remember the login, just log
again without this option and when you will
close your browser, it will log you out.

Cheers,
Yann Stettler