Ferrets do, indeed, use the litterpan, but they have to be trained to do it since they're often taken from their mothers before they can be taught about relieving themselves in a corner or specific place. Fortunately, training a ferret is easier than you might think.
First, you'll need to put a small litterpan into the ferret's cage. Young ferrets will need to stay in their cage most of the time when arriving at a new home for this reason. You should also avoid using the fine clay-based litters meant for cats since a ferret loves to dig around and rub themselves against the litter before exiting the pan. This can lead to respiratory system issues or anal blockages if clay-based litter is used. Use pellet-based litter from recycled newspapers or alfalfa pellets.
Don't leave the litterpan too close to the ferret's bed. Constant close proximity could lead to health issues later on. You can also take them to the pan while they're still in their hammock waking up for the day, but don't wake them up too suddenly.
Next, you should check to see if your ferret is already using the pan. Some take to the pan fairly quickly, others may need to be reminded. If your ferret is urinating or defecating in another spot that it prefers, move the pan over to that spot. Another good idea is to leave a little bit of feces in the pan to let your ferret know where it should go.
Whenever your ferret uses the pan, you should reward it by giving it a treat and lots of praise to show that this is good behavior. You should not resort to negative reinforcement, however, since it will often inhibit the ferret's ability to learn. If they do have accidents, gently place them in the pan as quickly as possible.
Once your ferret is using the pan on a regular basis, you can start to expand the space it's allowed to roam around in. At play time, you can let it scamper around a room, but you should have another pan ready nearby. A ferret won't take long from the time it feels it has to urinate to when it does so. A good sign that it has to urinate or defecate is that it's backing into a corner. If your ferret does this, move them to the pan immediately.
As your ferret uses the new pan more often, you can expand its range by placing more pans down in other parts of the house. Eventually, your ferret should have free roam over the house if you have enough pans. Anywhere your ferret may choose to use as a bathroom should have a pan in its place. If it's not somewhere you want a pan, then put it where your ferret goes and slowly move it over the course of a week.
Another good tip, especially in the early stages of training, is to place a bed somewhere if that particular somewhere isn't where you want your ferret to relieve themselves. Like other animals, they won't defecate where they're supposed to sleep or eat. You could even put their hammock there, and the smell alone will keep them from using that spot.