Welcome, limarymary.
In addition, it's a fairly big topic. Most teacher either take courses in how to teach grammar or they study at home on their own. The bookstore is a great place to start, and if there isn't one in your area that houses English books, you could try on-line sources, like Amazon.com or the great number of on-line grammar sites. It's a good start.
Is there a specific question about grammar that we can help you with?
All the best.