"Teach me how to cook cheap food."
That's a bit like "teach me how to ride a bicycle".

There are books that will teach you the basics of cooking. In the UK and Ireland we have Delia Smith and I'm sure her equivalent exists in other parts of the world.

How to make gravy? Gravy is served only with roast meat and it involves combining the fat from the roast meat with flour and browning the mixture over a hob, then adding meat stock (you'll probably use a stock cube mixed with boiling water) and reduce (meaning boil till some of the liquid evaporates)this over the hob till it's the desired consistency.

What you have been eating up to this isn't food, it's re-heated food-like substances. Your digestive problems probably stem from a poor diet due entirely to neglectfull parenting.

Have you considered bringing a case for 'parental neglect' as a means of raising some cash?