What is the meaning of the poem "Fork" by Charles Simic?

Two points to consider before we turn to your fine question. First, often a poem does not have a single answer, but is subject to interpretation. Second, consider the possibility that the poem's affect on you is its meaning. In this case, the strangeness and imagery of "Fork" would be its meaning.

 
And in fact, I'm going to argue that this is a large part of the meaning. In "Fork" Simic takes a close look at, well, forks, and forces us to do so. Look at a fork. It looks like a bizarre little pitchfork or, as Simic says, "a bird's foot." Do you really want to put that in your food? Your mouth? He makes the common world strange, and makes us like kids or aliens, seeing things for the first time.