She meets a whole cast of other characters as well: the Good Witch of the North, the Munchkins, the Wicked Witch of the West, and, of course, Oz – who is not who Dorothy thinks he is. Throughout it all, her faithful dog, Toto is at her side.
Baum was in part inspired by Lewis Carroll’s Alice’s Adventures in Wonderland. Carroll rejected the Victorian notion that children’s books ought to be moralized; instead, he contended that they should be fun & pleasurable to read, with pictures and a main character that children could identify with: a child, like themselves. Baum took that to heart and wrote a fun book that, in the end, was enjoyable for both children & adults
You can get a full hardcover set of the books here. The 1939 film is critically acclaimed; and Wicked tells the story from the perspective of the Wicked Witch of the West. If you want to learn more about the world of Oz, Yellow Brick Road and Beyond is a documentary available on Amazon Prime that should help give you some insight.