I am 24, male, and i don't have beard, less muscle and look like an 18. i got my testosterone tested it came 374ng/dl. how can i improve it?

Your testosterone level is still in normal range, especially if it was not checked in the early morning. Muscles can be improved with diet and exercise. Beard and body hair are strongly affected by your family's genes.

First recheck T level and note time of day. It varies considerably around the day. Always send normal values for your lab. I would also look at all males in your family tree to see their beard growth and body size. It often runs in families.