Anyone with a University of Bath username and password will be able to log into Moodle.
Moodle can be found at: http://moodle.bath.ac.uk. Upon navigating to this page, you will be prompted for your username and password.
There are caveats to this, however; for example students who have not yet paid their fees, or who are not yet fully registered etc. will not be able to access the system.
If you (or your students) are unable to log into Moodle, a support request should be sent to the Computing Services Help Desk via their web form located at: http://www.bath.ac.uk/bucs/help/contact/index.html