Shouldn’t this be, “You need Tom here”?
This sentence means “Tom needs you here”. Because нужен isn’t a verb but an adjective.
Literally it means: For Tom, you are needed here.
“For Tom” uses the Dative case (therefore the y at the end of Тому), and “you” is accusative.
You have a few other similar “adjective-verbs” in Russian (can, cannot, need, must, and so on).