How do you make pasta bake?
There are lots of different kinds of pasta bakes on this site if you're searching for a specific kind of recipe.
If you're trying to figure out how to actually create your own, the easiest way to get one started is by making a bechamel sauce: Melt 3 tbsp. butter in a saucepan. Whisk in 3 tbsp. flour and cook for a minute or two. Whisk in 2 1/2 cups of milk. Cook, stirring frequently, until thickened enough to coat the back of a spoon. Remove from heat. Season with salt and pepper, and whatever other add-ins you like.
Figure 1 pound of pasta to 1 recipe of bechamel. If you add lots of veggies or meats (more than a half-pound, I'd say), then increase the bechamel by half. (If you like, you can use broth or stock for your liquid instead of milk (then the sauce becomes a veloute instead of bechamel).
From here, you can experiment with any kind of add-ins - whisk 1 pound of shredded sharp cheddar into bechamel for a great cheese sauce, or whisk 3/4 cup grated parmesan into bechamel or veloute for a light, sharp sauce. Substitute 1/4 cup of your liquid with wine for a little different flavor. Chopped fresh herbs, mustard, worstershire, hot sauce - play around with it.
Once you've got your sauce down, you can experiment with building your own bakes/casseroles. I like to make a bechamel with salt, pepper, parmesan and nutmeg, then combine with cooked pasta shells, broccoli, and cubed ham. Sprinkle with fontina and bake at 350 for about 20 minutes.
Here is my favorite one using tomato based sauce with sausage and cheese.