Bechamel is a simple white sauce that can serve as a base for cheesy macaroni, creamy queso dip, white lasagna and all sorts of gratins. It's deceptively easy to make, and the above video can walk you through it.
First, you'll need to melt some butter (about 60g) without cooking it even a little. Add the same amount of flour and whisk until you get a smooth paste. Cook for a minute, without browning, to get rid of that raw flour flavour, then gradually pour in hot milk, whisking all the while to prevent lumps. Bring to a simmer, add some salt and just a bit of fresh nutmeg. To make a tasty cheese sauce, just chuck some cheddar and/or Gruyere in there. You can use that as a dip, stir it into macaroni or layer into casseroles.