Vitamin C SOS!!

I'm still learning skincare and I can't see the forest for the trees at the moment 😵‍💫 so I need your help!! 🙏🏻 I received this Sephora vitamin c+e serum and want to use it. I'm trying to find out what other ingredients you can combine but see a lot of contradictory things; no niacinamide, just with niacinamide, spf anyway, sometimes no sunblock/sunscreen 😬 What are your tips for using vitamin c serum?

Translated from Dutch by AWS