Béchamel sauce sounds like something all fancy-schmancy that you might never have reason to use, but really it's just the French word for "white sauce" - and an important ingredient in many French recipes.
And you just MIGHT have reason to use it, even if you don't do any "French" type cooking. In scalloped potatoes, or white lasagna, or creamed peas and new potatoes, or Moussaka, or creamed spinach. You'd be surprised.
You might also be surprised how easy it is...
2 Tbs. vegan margarine (I prefer Earth Balance)
2 Tbs. white flour
1 1/4 Cups UNSWEETENED plant milk of your choice
1 pinch salt
In your trusty cast-iron pan, melt the margarine on medium heat.
Add the flour and whisk to form a "roux". (What is a "roux"? It's a paste of flour and fat that you can cook a little or a lot, depending on the color you want your finished sauce.)
Whisk over medium until the roux darkens to just BARELY golden-tan, or just a few minutes.
Add the milk slowly, whisking as you go, making sure there are no lumps.
Remove from heat after the sauce has simmered and thickened into a smooth gravy-like sauce.