You have a story idea, some basic plotting ideas, and a few setting ideas. Now you need to develop your characters. The process isn’t quite as intense as actually giving birth, but close.
Each character (protagonist, antagonist, villain, sub-characters) needs to be unique from the other characters. You don’t need to go into a lot of effort in creating the side characters. The focus of this “birthing process” should be on the two main characters and possibly the villain. A good villain needs to be as fully developed as your main characters.
I have already gone into the importance of picking the right names for your characters, see the previous post and the Writing Tip about The Art of Naming Characters. Now you need to learn about each of these characters, before the readers do. Sometimes you are going to learn (create) a lot more about these characters than the reader will ever know about. But the more you know about your characters, the easier you can picture them in your mind as you write their story. This is particularly important when you are a beginning writer. The more experienced writer learns what facets of their characters to agonize over and what may never be important enough to think much about. So my focus here is more for the beginning writer.
I am adding an article today on Making Strong Characters to the Writing Tips on the blog and to the Writing Tools on my website. This will give you some basic tips on creating a unique character and for showing strong characters. Along with this I have added some of my favorite templates for character creation: Character Contrasts, Character Grid, and Character Grid with Villain. There are numerous websites with articles on creating character sketches, but I believe the basics are covered in my article and templates.