Too vs. Two vs. To

Too means "also" and is generally used at the end of a sentence. "Too" also indicates too much of a particular quality.
That car is too expensive for me!
I'd love to come to the party, too.

Two is the written form of the number 2.
There are two applicants for the job.
She has two cats.

To is generally used as a preposition. It is also used as part of the infinitive form of verbs.
I gave the book to him.
The verb "to understand" is irregular.