To is a preposition that indicates movement or action towards a place or direction, or a relationship between two things. It can also be used as an infinitive marker to introduce a verb. For example:

• She is going to the store. (preposition)
• He gave the book to his friend. (preposition)
• To err is human. (infinitive marker)

Too is an adverb that means also or in addition. It is used to indicate that something or someone is included in a group or action. For example:

• She is coming to the party too.
• He wants to come too.

Two is a numeral that represents the number 2. It is used to indicate the quantity of something. For example:

• She has two cats.
• He has two brothers.

In summary, to is a preposition that indicates movement or action towards a place or direction, or a relationship between two things, and an infinitive marker to introduce a verb, too is an adverb that means also or in addition, and two is a numeral that represents the number 2.