I suggest glass cages, like a big aquarium. Most of the time, hermit crabs come in wire cages, especially if you get them from some mall stand or some store on the boardwalk (which is where I got mine). They really cannot live the best life in this cage due to the fact that hermit crabs need constant humidity because they're native to tropical climates. The species you most likely have are called Caribbean Purple Claws, and as they are from a tropical area, they need good humidity, or humidity is ideal.

Right now, mine are in a 2.5 gallon tank, but if I had the room, they'd be in a 10 gallon glass aquarium which you can find for around $14 at Walmart or Petsmart. Gravel isn't good material for hermit crabs. You need either sand or coconut fiber substrate, which they also sell at Petsmart. Generally I recommend a mix of both and at least 4 inches deep, if not deeper. Purple claws are land crabs and they LOVE to dig, especially when in molt so it needs to be pretty deep for them. They also LOVE places to hide and logs to climb on, for that I suggest logs with holes in it or Choya wood!

To keep humidity up, I suggest getting a heating pad for at least half the cage (they have hermit crab ones but also sell them for reptiles). I don't suggest a heat lamp as you don't want it too hot because it stresses them out. A temperature gauge is a good idea for keeping track of how hot it is in the tank. They like 75-80 degree F, generally.

Feeding can consist of many things. I give mine things like Turkey, fruits, veggies, and hermit crab food. But if you keep it in too long, you'll attract mites, fruit flies, so just be careful of that! Another thing you want to be careful of is MOLD. I've had it grow before on my logs because it becomes a little too humid in their tank at times. Mold can spread everywhere once on one surface, so be careful to give them some air circulation (crack the tank open a few hours a day).