It's shaped differently from camp ovens common in the United States; The round shape allows heat to flow evenly around the sides and maintain liquids at the lowest point to keep from burning.
Because the legs are longer than camp ovens, more coals are required on the bottom for potjies, than for camp ovens.
Potjie means "small pot", but not all of them are small.
The sizes are a bit confusing; The size number does not mean amount of quarts.
Size 1/4 is a half liter, and 4 inches.
Size 1 is 3 liters and 10 inches.
Size 2 is 5.8 liters and 11 inches.
Size 3 is 7.8 liters and 12 inches.
Size 4 is 9.3 liters and 15 inches.
Potjies are used to cook potjiekos, or "small pot food". In other words, stew*. Usually meat, veggies or fruit, and potatoes, pasta or rice, slow cooked with Dutch seasonings. Originally, bones were included to thicken the stew.
*Mostly stew, but it's come to mean anything that's cooked in a potjie.
Potjies are often the center of social activity, similar to crawfish boils in cajun country, or pig roasts in Texas. Guests mingle as the food slow cooks.
If you don't have a potjie, any potjiekos recipe can be cooked in a regular dutch oven, and you can still cook it outside and have guests over!
And as soon as I actually try a recipe, I'll post it.
Potjies without legs are called "plat* potjies", and you can use them on the stovetop. They come in sizes 1 to 3. Sometimes they're used on camp stoves for bread or dessert.
*No, that's not a typo. It's plat, not flat.