1. First, you can edit the "Learner" user-type (1), through the administrator's interface under the User types option. To do so, you must un-check the option "acquire courses" (2) that is located under the learner's permissions and "Course catalog" section. In this case, you will be responsible for assigning the courses to the users.
2. You can assign a price to your courses *and* set up your eCommerce processor through the Account & Settings->E-commerce tab (1). The users will then be able to select courses through the catalog but will have to purchase the courses in order to have access to the material provided.