Where is the link for registration?

When you are logged in, go to design, then widgets, and you should see one called Meta: Log in/ Register

Just move that to wherever you want it on your sidebar.

Thank you, but it does not say log in/ register, it only includes log-in with some other options.

latestart,
First, go to your dashboard > Settings > General and make sure the “Anyone can register” box is ticked. See if that does it.