Sign up and log in pages

I am new to WordPress and I am trying to build a site sub-domain for a church for bible classes and need to add a sign up and login page or widget to give access to different people, I downloaded a theme named Blogs MU. Could you please point me in the correct direction in order for me to learn how to add this and also to be able to add more pages all link to the sign in.
The site is
Thank you for your help and support.