However is a conjunctive adverb used to introduce a statement that contrasts with or seems to contradict something that has been said previously.
Common usages of however:
1. To show contrast: "I wanted to go; however, I was too tired."
2. To indicate degree or extent: "You may do it however you like."
3. As an intensifier meaning "no matter how": "However hard I try, I can't solve this problem."