These words look similar and sound alike, which is why they’re often misused. Once you know the difference, though, it’s easy enough to make the right choice each time.
"Too" is an adverb. It can be an intensifier, a word that adds emphasis. Sometimes it indicates excessiveness:
You plan too much.
It can also mean "very" or "also":
She wasn’t too pleased with the results.
Linda wants to go to the park too.
"To" is more versatile. It is a preposition, a word that links a noun or pronoun to the rest of a sentence:
Take me to the airport.
She submitted her resignation to Mr. Fleiss yesterday.
"To" may also play a part in an infinitive, in which "to" is linked with a verb in its simplest form:
She’s learning how to draw.
He tried to hold her hand.
Once you have the rules for "too" figured out, you’ll use "to" for most other instances. Except, of course, when indicating a number, in which case you’d use "two.