Essentially, it's like a giant chicken with a "deeper" and more distinctive flavor. The main reason I like them (other than the flavor) is the sheer quantity of meat you can get from one roasting session. One could roast multiple chickens for a similar effect, but with a turkey you only have one skeleton to pick meat off of, so it goes faster. Leftovers can be frozen and/or reused in all sorts of ways (sandwiches, soups, casseroles, etc.).
The breast meat of turkey is a little different from chicken, but they have a similar texture and both tend to be rather mild in flavor compared to game birds. If you had access to a wild turkey, the meat will be gamier. The dark meat of the turkey (particularly legs and wings) is generally much more flavorful than chicken, with a "deeper" flavor that some people love and others dislike. (This may be the reason for the increasing popularity of whole turkey breasts sold by themselves in the U.S., which can be roasted like a whole bird, but don't have the "other parts" that are seen as less desirable by many. The vast majority of people I know tend mostly to eat turkey breast meat, usually served with gravy and stuffing.)
I've seen turkey wings and legs sometimes offered at Southern U.S. BBQ joints; when slow-cooked, they are a bit of a "Southern delicacy." On most farm-raised turkeys I've had recently, the thigh meat doesn't have as much of that "rich turkey" flavor that I seem to recall in the past, but it has a more distinctive flavor than the breast meat. Internal organs ("giblets") also tend to have a stronger flavor than chickens, if you're into eating livers, gizzards, hearts, etc.
There's often more fat in various parts of the bird than in typical U.S. chickens, which adds to a richer flavor. However, there's usually not as much fat as found in other common U.S. poultry (particularly duck and goose).
When prepared and ready to buy at a butcher, turkeys essentially look the same as any large poultry. They are often much larger than chickens, easily going to 20 lbs. (10 kg) and more. There are some differences in proportions and details that you'll see when cutting up or eating. In particular, the legs and wings have a bit more connective tissue and bony/cartilage bits than a chicken, since it's a larger bird and needs more support. This also tends to make the leg and wing meat a bit "stringy," which may be the reason for the slow-cooked versions I mentioned above, allowing time for the meat to break down more than when just roasting the whole bird. The meat is also a bit darker in color than chickens, particularly noticeable in the "dark meat" sections.
If buying a whole bird, most people in the U.S. essentially prepare it as they would make a large chicken, which usually means roasting in the oven. They are usually cooked at somewhat lower temperatures than chicken, to give time for the whole turkey to cook without drying out the exterior. Given the long roasting time for such a large bird, there's been a bit of a trend recently to cut up the turkey so it lies flat ("butterfly" or "spatchcock"), which allows it to cook faster and potentially more evenly.
Other than that, one can often buy individual turkey parts and use them in similar ways to chicken parts, keeping in mind the longer cooking time required. They can also be used (as with other poultry) for soup meat, etc.