English teachers cover a wide array of subjects including grammar, reading comprehension, and written and verbal communications. If you're thinking about teaching English you also need to determine what grade level students you want to work with, and whether you want to teach students who speak languages other than English as their native tongues.
Grammar is one of the fundamental elements to understanding any language. As a student learns to read, speak or write any language, he also needs to understand basic elements such as sentence structure and verb conjugation. In addition, students need to understand concepts such as capitalization and punctuation and even the American English alphabet. English teachers help students grow at all levels of their educational development. Teachers who work with younger students help them develop the basics while high school and college level teachers help students develop communication skills they will use for the rest of their lives. Some English teachers even get to experience the joy of helping students to find their natural talents for writing and speaking the English language.
In addition to teaching the standard English curriculum, you might also want to consider teaching English as a second language. This is a challenging career choice as many students already have developed language skills in their own native tongues. Many ESL students don't get to practice their English skills at home, which can make it more difficult to teach them. With all these challenges, many people find ESL instruction to be quite rewarding.