OK, it may sound simple, but making sauces always seemed to be a gigantic mountain to me. They don't have to be, though. I researched making a cheese sauce (we had asparagus recently and I can't do asparagus without cheese sauce). Here's what I did.
Cheese Sauce
2 Tbsp butter (use the real stuff - it's cheese sauce, not exactly low calorie)
2 Tbsp flour
10 - 12 oz milk
2 - 3 cups shredded cheese - I used a mexican blend for it's meltability - can use cheddar or colby - you choose.
salt and pepper (use white pepper if you don't want your family/guests to see it in the sauce)
Directions:
Melt butter in saucepot over medium heat, add flour and stir to combine - but do not cook it to where it gets any color. [FYI - this is a roux, a thickening agent used in making gravies and sauces. But you may not know, the darker the roux, the less it will thicken your recipe. Cajun cooking generally uses a roux that is has been cooked to a dark color - it isn't there to thicken the gumbo, it actually adds a flavor component instead.]
Sorry, was off on a tangent. Slowly pour in milk, stirring with a whisk (if possible). Cook until mixture starts to bubble and thicken. Cook 2 minutes, remove from heat for a moment. Add in cheese and stir until it melts. Place back on heat until fully melted.
Yields about 1 1/2 to 2 cups sauce.