Your course is built by adding activities and resources for student learning.
In Moodle, a resource is something that students access for information and support, but have little direct interaction with, such as: files, PowerPoints, web links, videos, etc.
An activity, on the other hand, is something that students work with directly, whether alone, with other students, or with the teacher. Activities allow for grading and generate a grade item entry in the grade book. These can include: quizzes, forums, assignments, etc.
The Add an Activity or Resource link has changed somewhat in Moodle 2. The separate drop down menus have been replaced by a single link, which opens an activity and resource picker. This is only seen when editing is turned on.