Cactuses need lots of sun. A bright, southern facing window at the very least. When the soil is dry several inches down, give them a good soaking and let them go dry before the next watering. Don’t fertilize cactus.
Christmas Cactus or Easter Cactus is one of the few cactus that needs water when the soil is only dry down an inch or so. It will not mind if you let it go a bit longer. Flowering in the winter around Christmas (or Easter ) it will brighten up the house in the winter. It does well in a hanging basket having vine like rather than upright growth. To propagate it just trim off a few leaves and put them in a moist soil and they will root in a month or so.
There is not much to say about care of cactus. They are low maintenance plants. Stick them in sandy soil, put them in a sunny window and water infrequently. Cactus do well in dish gardens. I’ve also had them grow to full size in homes given a sunny window.
I had a black lab who ate everything and anything, including several house plants. One evening he ate my tall, pointy cactus. It did him no harm and it cured him of eating house plants.
Be very careful not to overwater cactus and succulent plants especially in the winter when they are not getting much light. Black or brown spots on the cactus or succulent are a sign of over watering.
If you have black or brown areas that are mushy, that is bacterial soft rot. Remove those sections with a clean, sterile knife. Let those sections air dry. Also see How to save your plant from soft rot
Sometimes brown scab like things will form on your cactus. We really don’t know why this happens. it is possibly related to spider mite damage or too high of a humidity for cactus plants.
Mealy bugs can also bother cactus.