I'm new to the gardening world and have recently just brought a cactus and some succulents. Could you please identify them (what kind they are) and give me any tips on how to keep them alive. Thank you. Btw they usually live on my window sill but I'm worried they aren't getting enough sun.

Moved the Plant ID forum

The first one is Mammillaria vetula subsp. gracilis 'Arizona Snowcap'. It is a very spiny version of the normal plant.
The second looks like some kind of Euphorbia.
The third one looks like some form of Echeveria, but someone with more experience with those kind of succulents (I have trouble getting them through the summers here in Arizona, so do not grow them) will have to confirm that.