Now you have some choices. I cook my dressing in a Crock-Pot all day while I prepare the rest of my meal. It comes out moist and perfect, and it doesn't take up oven space. I can keep it hot all through the meal and just take small serving bowls to the table as they're needed. It's a great way to cook the dressing!
But if you're a traditionalist, you can pack the dressing inside your turkey to cook with the bird. However, authorities are telling us that's pretty risky these days. You can bake it in a casserole in the oven. If you do it that way, seal it with aluminum foil so it doesn't dry out. I don't bake mine, so I can't say for sure how long, but I'd estimate about 1-2 hours at 350 degrees. It should be very hot in the middle before you take it out.