How to use any acne cream depends on the medication type, the severity of the acne and its location, and a host of other factors.
But some general rules of thumb are: Apply directly onto clean, dry skin. This allows it to be cleanly absorbed, increasing its efficacy. The only exception is with retinoids, which can sometimes be applied after moisturizing to help combat any resulting dryness. Apply moisturizer after applying acne medications. It helps the product better penetrate your skin, and helps prevent your skin from drying out. Sunscreen should be applied last, helping protect your skin from sun damage.
Handy tip: if unsure which of your products to apply first, try going from thinnest to thickest. This helps topical creams permeate the skin properly.