The adjective natural is a common word with a lot of meanings. It describes anything that comes from nature, but it also means "inborn" when you describe your basketball-star friend as a natural athlete.
To be/act/look natural is to be normal and relaxed in the way you behave and look. I'm going to take your picture but don't pose— look natural. Try to be/act natural. She was adopted immediately after she was born and never knew her natural [= (more commonly) birth] parents. He is the natural choice to succeed his father as company president.