One of my favorite plants ever is the Euphorbia Ingens. In the wild, they grow into huge trees, but in a container they look more like saguaro cacti straight out of Arizona. They will immediately turn your home into a desert oasis.
They are not difficult to care for, but they need a lot of light. They require at least 4 hours of bright light daily, however they can burn if in strong direct light so its usually best to keep a couple feet away from a bright window unless acclimated to direct light.
Water deeply when the soil dries out. In the summer this might mean 1-2 times a week, in the winter this might mean once a month. You can use a water meter or test it with your hands.
They need chunky soil for proper drainage. It's likely it will come this way when you purchase one, but make sure you stick with it when it's time to repot.
They don't need to be fertilized often, just once in the spring and once in the summer.
Brown spots can be a sign of sunburn or rot. If it is squishy, this is rot and it will need to be cut off before it spreads (rot is due to overwatering and/or low temperatures).
**Be very careful when repotting! Aside from the spikes, euphorbia have a toxic sap that can irritate skin. Be sure to wear thorn proof gloves when handling. They are also toxic to cats and dogs so are not recommended if you have pets.