How to use liquid compost
 

If I've got some compost (mostly anaerobic) that is a few years old (composting in a garbage can), and just happens to be in liquid form for some odd reason, how much of that can I give to a very nitrogen-starved, transplanted tomato (not recently transplanted) that is a few inches tall? Do I just water it into the soil?

It smells like cow manure when I stir it. Is that normal? It's from fruit, produce scraps and such.

No, it's not normal for it to smell like cow manure. Being anaerobic, I wouldn't use it. Anaerobic bacteria can produce some nasty metabolites that are harmful to plants in stagnant wet compost. It won't be useful for N either.
Best thing to do with it is dump it in a pile with some fresh inputs, turn it once in awhile and let it become aerobic. Eventually it will smell like fresh fertile soil.