A singer is a person that uses their voice talents to make music. Often in a band a singer is required to share the lyrics. There is a range of voice types that will describe a singer. For example females can be soprano, mezzo soprano, or contralto. Males are countertenor, tenor, baritone, or bass. In a rock n roll band there is usually one singer or more.
The leader singer is going to perform most of the lyrics for the audience with some backup vocalists. Professionals will go through voice training at some point in their career. Many rock n roll singers begin their career without training, but once they become popular will go through the proper training to make them a lot better.