silly question about customer log-in and registration

Okay this is probably under the header of stupid questions, but... I am trying to get my site organized and put a link to register as a user for the site. Is there a short-code for this? a widget that I am missing?

My site sells downloadable products, and I would like users to be able to go back to their previous transactions and download the products again if they are logged in, a page I normally call "My Library", is there a short-code to send them to the right page for this?

Thanks!
Amy