A teacher is a person who helps people to learn. A teacher often works in a classroom.
There are many different kinds of teachers. Some teachers teach young children in kindergarten or primary schools. Others teach older children in middle, junior high and high schools. Some teachers teach adults in colleges and universities. Some teachers are called professors.
Teachers are usually professionals. They have been to college and got qualifications. They use various methods to teach. Teachers explain new knowledge, write on a blackboard or whiteboard, sit behind their desks on chairs, help students with their work and mark students' work. They may also use a computer to write tests, assignments or report cards for the class.
Teachers are not always professionals. Parents usually do a lot of teaching before children ever get to school.