Well, ignoring the fact that it should come with instructions and usually a small recipe book, you just use it like a big stew pot. It is very cheap to run.
For example, get everything ready for a stew; cubed beef, sliced and diced veg, maybe a tin of lentils or beans. Put the whole lot in, a packet of oxtail soup made up (1.5 pints is best to cover the ingredients) stir. Switch it on medium as you leave for work When you get home around 8-9 hours later your dinner is ready.(Use high setting if out for less time.) Just do a few spuds.
This will easily feed 4 adults. I use fairly cheap stewing beef and a long slow cook tenderises the meat beautifully. It also makes a great rice pudding. Use favourite casserole recipes as well.