Too/to
"Too" is an adverb, and "to" is a preposition.
"Too" is also used in a sentence such as "There are too many cooks in the kitchen."
How many are there? I don't know, but too many. Definitely more than two. And I'm going to give hell to all of them."
"Two" is a specific number. "Too" might be thought of as an indefinite number, or as CatchC says, an addition, whether it's "I'm going, too," or "We're going, too." "To" isn't a number at all.