Cheryl, your question is too broad, so people don’t know how to answer it. “To” and “at” are both prepositions, but they have many different meanings and are used in many different contexts. If you really want to know all their diffrent meanings, then you can look them up here: www.oxfordlearnersdictionaries.com/

thanks a lot .

You haven't given any examples, so we can talk about the common ways each of the words is used in relation to a place. Where are you going? I am going to school. Where are you? I am at school.