Easy one first: two – two is always a number. Use two when you are referring to a quantity that is greater than one and less than three.
The confusion or errors usually occur between to and too. To has multiple meanings nearly all with the idea of in the direction of or moving toward a certain point. It is used either as a preposition or infinitive. Prepositions are those oh-so-useful connecting words like for, of, at, by, since, etc. They connect or link an object and what comes before it to show the relationship between the two. For example, Joe took the car to the shop for repairs. To (the shop) is the preposition connecting car and shop; for is another preposition connecting or showing the relationship between shop and repairs. The object of the preposition can be either a noun or pronoun, as in “Mom took him to the woodshed.”
To also functions as an infinitive—a verb phrase. “Jennifer wanted to go to the party, but mom said no.” To go is an infinitive verb phrase, again with the meaning of moving in a direction.
Too is an adverb meaning to an excessive degree. “It’s too hot in Florida in the summer time.” It can also mean in addition or also. “I gave a candy bar to Tom, too.” Here’s a simple way to keep these two little words straight: when you want to indicate more – add an o to to. Now, that’s not too hard, is it?