I'm going to use the word 'some' or other vague words as I am pretty clueless about amounts. Might be worth having a look at some recipes online to get an idea of relative quantity. I tend to vary the amounts too, but that's the beauty of this recipe, its really hard to make it inedible!
Put some green mung beans - in the photo, I use the packet shown, but this makes huge amounts. You might want to start with small quantities and working out what you like -into a saucepan, put plenty of water (I have about an inch and a half on top of the beans - it will soak it all up and then some), bring to the boil and them simmer.
While that is cooking, chop up, or grate some ginger and garlic, and throw that in.
Put in some chopped tomatoes (I have varied the amount of tomatoes wildly and it never seems to make much difference).
Add some hot pepper (we put in a whole Scotch Bonnet and let it cook in there but that might be a bit too mad for most) or not. You can always add some hot sauce at the end, when you eat it.
Add some ground tumeric and ground cumin (roasted cumin is best). there is traditionally a stage where some oil is heated in ladle, and the whole or ground cumin is 'burnt' in there and then plunged into the dhal but I'm happy without this stage (and makes it healthier and safer!)
Just let it carry on cooking, and add water until its a mushy texture. Salt to taste.
Serve with rice, or I have even watered it down as a soup. A tomato and onion salad can go nicely, or some cucumber.
Good luck!