Characters are the central element in any kind of storytelling. You can learn all about creating characters in the Gotham Character course. And you can also start the process right here on this page.
One of the best ways to get to know your characters is to ask questions about them. Many writers do this as a kind of homework before they actually start writing a story. The more you know your characters, the fuller they will be. This might also make your story easier to write. The following questionnaires may be downloaded so you can work with the actual documents.