No problem… I will try to explain it here. First lock down you content for everyone.
1. Navigate to the “Manage Content Protection” tab under the “Membership Levels” menu.
2. Select the “General Protection” from the drop down menu.
3. Click on the “Categories” tab to bring the categories you have.
4. Select all of them and hit “Set Protection”. This will make all the posts under these categories protected.
Now that you have the content locked, you can start giving access to particular categories depending on membership levels. Lets do the following:
1. Select the “Free Membership” from the drop down (given you named your free membership level “free membership”)
2. Click on the “Categories” tab if it’s not selected already.
3. Check the checkboxes next to the categories that you want to give your free members access to.
4. Hit “Grant Access” button. This will make it so your free members will be able to access the posts under the categories you selected in step 3.
5. Do step 1 to 4 for the “Premium Membership”.
Do a quick test to check that all the protection is working as expected. Let me know if this helps or if you need more explanation. The following URL on the documentation site should have some explanation on this too: