How Do I Learn To Cook Without Wasting Food?

I can cook some things like crab rangoon, tuna casserole, easy stuff. I want to cook the dishes my mom makes and other recipes (she shows me but she always estimates the time and amount she puts in which is hard).
I want to learn to cook but I’m afraid I’ll do terrible and the food will go to waste, I hate wasting food. Any advice? Oh, and I’m always too lazy with no motivation to cook…I always end up buying some fast-food or my mom’s left over cooking.