"To" is generally used as a preposition. For example, "going to the park".
"To" can also be used in the infinitive form with a verb, eg. "to walk" "to swim" etc.
Whereas, "too" is normally used to mean the same thing as what was previously said. Eg. someone says "I love pizza" and you could reply "me too", in which case it sort of acts as a synonym for "as well".
Another use for "too" is to say that something is in excess, for example there are "too many" or "too few" things, for example.
Sorry for the poor explanation - I hope it helps! :)
