Scratched my car, what is the best way to repair it?

Could you take a picture of it from a couple angles and post them? Paint repair depends a lot on the actual damage and how bad it is. There are various methods used and how DIY friendly they are also depends on what needs to be done.

That looks like it's a gouge in the plastic trim. Normally for that you would sand the area so the edges of the gouge are smooth and tapered, then you use a special filler made to repair plastics like trim and bumper covers. Then sand that smooth and repaint. The issue is usually matching the exact shade of black. The other is that the special filler is expensive if you buy it in small amounts. Your best options are to see what a local body shop would charge for the repair, then look to see if replacing that piece is cheaper than a repair.

It can be hard to find sometimes. Polyvance 2000T is one U-Pol 7061 is another.