To is one of the most useful little words in English, serving several important purposes:

1. It shows direction or destination. When you walk to school, ride your bike to a friend's house, or throw a ball to your teammate, you're moving toward something or someone. The word points to where you're going or what you're aiming for.
2. It marks the beginning of an infinitive verb, which is the basic form of an action. To run, to think, to build, to imagine: these infinitives name actions without saying who's doing them or when. When you say “I want to learn Spanish” or “She needs to practice piano,” that little to signals that a verb is coming.
3. It can show a relationship or connection between things, as in “the key to the door” or “the answer to the problem.” It links one thing to another in a way that shows they belong together.

You use this word constantly without thinking about it, but to works hard in almost every sentence you speak or write.