Enrolment

Hi,
I am new to Moodle and testing a new installation. When I log in to Moodle as a student, I am able to see all courses without enrolling. Did any of you ever experienced this before, and would you know how to require enrollment for the courses?
Any help would be appreciated.
Thanks!
Max

Note: The idea is to set up payments with paypal, but the problem persists whether or not I enable the paypal course enrollment plugin or set it as default from the site administration panel when I am logged as admin.