If I understand you correctly, you want the navigation on your Moodle site to only list the Courses and Categories without the Activities. You can set this by editing the Navigation block to show only Courses and Categories. Editing will need to be turned on first. See the image below.
I also have a tutorial on how to edit the navigation block here. If you are referring to a different area in your Moodle please let us know the exact spot you want to remove the activities on and we can look further.