Use your azelaic acid product once per day, either in the morning before your sunscreen or at night, before your moisturizer.

Use every day, as many times as needed. For most people, it's best to use a moisturizer twice per day. In the morning, apply it before your sunscreen (or skip the moisturizer in the morning if your sunscreen feels hydrating enough). In the evening, a moisturizer is usually the last step of a routine.