Anything done individually happens one at a time, separate from others. In baseball, each player bats individually.
An individual is a single person, or you can refer to an individual thing, which is one thing. Likewise, anything described as happening individually happens one by one or separately. An only child is raised individually. Doctors usually see patients individually, not in groups. If you're in a single-file line, you're lined up individually. Think of the number one when you see or hear the word individually.