I bought two cacti from IKEA. I water them weekly. They seem happy. Not growing much but maybe a little. I don't know what they are or if I'm looking after them right. Please have a look at the pictures and help! Thanks!
These are cacti from the genus Mammillaria, which particular species I don't know (the genus has a lot of species). Best is to wait for the flowers, then it will be easier to identify which species it is.
Cacti like a lot of sun, so a window facing south would be ideal (if you live on the Northern hemisphere that is).
Also they don't like a lot of water, once every 3 or 4 weeks would be okay. Try to get the soil to dry up between waterings. In winter, try to put them in a cool place and don't water them at all for months.