they are both used in conjunction but "however" is a little more power full and can be used at the start of a sentence some times. We went to the mall, "but" it was pact so we left early. However you look at it; its the same old thing. jimmy went to the mall; however, he never told his mom. If you use however at the beginning of a sentence and don't insert a comma, however means “in whatever manner” or “to whatever extent.”