YOM is used mainly to express satisfaction, like in good food, and is similar to the word yum, but prounounced yawm, instead of yuhm. It also can be used to indicate anything that you are thinking about or anything that may interest you.
It originated with an asian male who ate burgers and said 'yom' to express the goodness of the burger, but then went on to point out things with using it. The proper format is to say 'YOM', then whatever else you may be thinking of. It is best to keep whatever you wish to say after YOM to a maximum of three words to keep the phrase smooth and not awkward.
Girl 1: Look at that guy and girl over there making out!