Think of it this way: your serum is the treatment, your moisturiser is what makes it stick.
After cleansing, apply your serum to freshly washed skin. Let it absorb for a minute or so. Then follow with your moisturiser to seal everything in. That's it, two steps, two products each with their own roles, and you're done.
If you're using a facial oil like the Renew Facial Oil or Hemp Balancing Face Oil, those generally go on after your moisturiser or can replace it depending on your skin type, a good rule of thumb is that oils go last.