This is an old  (well, from when I was a kid) family recipe and I'll apologize up front for not knowing quite what quantities to tell you, but it's easy to judge as you go and my first cooking lessons were from my mom, who almost never made the same dish the same way twice, but somehow always made it taste good. 
Making baked macaroni and cheese is kind of an art. 
It's a simple dish that can be made as fancy as you want to spend the time making it. 
This is an easy method that isn't fancy, but tastes great. 
Start by cooking your macaroni.  You can use any shape of pasta, but the purist in me like to use the good old elbow macaroni.  Drain it well and set aside.
Pre-heat your oven to 325 or 350.
Spread some butter on the bottom of a glass baking dish, I generally use a 9X13 corning ware dish.
Toss the pasta, cubed or sliced Velveeta and can of stewed tomatoes in and mix them up to evenly distribute everything.  Mix in some milk to give the cheese sauce a creamier consistency. 
Top with slices of cheese and a few pats of butter. 
Bake until the top gets lightly browned.  (about 20-25 minutes)
Serve with some peas and you have the meal eaten in the Berry household several times a month when I was young. 

Baked macaroni and cheese:
1 box of pasta, elbow macaroni or shells work best
1 box of Velveeta cheese
about 3/4 cup of milk
1 can of stewed tomatoes, drained of most liquid, but still moist
butter or margarine