Litter training is relatively simple, but every rabbit's situation is unique. The methods you use for training, the types and locations of boxes you choose, and the type of litter used will all depend on your particular needs. Rabbits can be litter trained at any age, but adults are easier to work with than babies because their attention span increases as they grow older. When they reach the age of 4-6 months, their hormones become active and they begin marking their territory with urine and feces. Spaying or neutering will increase the likelihood of using the box.
Training takes time and patience, but is well worth the investment.
The great thing about rabbits is that they are instinctually tidy housekeepers. Rabbits tend to prefer corners, and will use the same spot over and over again. They are very habitual and routine-oriented animals. When training a rabbit, it is important to listen to their needs, too. If they insist on using one spot, you will need to accommodate them.