how to layers active ingredients ?

okay wow. So first of all I would start with ONE active and slowly introduce it before using a another one! I would incorporate the vitamin c in the AM. Use this at least for like 2 weeks (?) depends on your skin. But if you feel like that your skin fine then I would start another one. In the PM I would use Lactic Acid first and then Glycolic Acid. I guess you're new to this and the Lactic Acid is more gentle so great for beginners. I would use Retinol in a few weeks or months after that. Because the Retinol you bought is a really strong one. Just please be careful and use all these slowly.