Go for it!
Nobody is born published. Not even the Nobel prize winners!
I usually start with my characters. They need physical descriptions, mannerisms, quirks, and back story. You need to know about their childhood, their family, their sexual history, their career history, their beliefs and values. They need traits, goals, and a flaw. Goals, whether they be conscious goals or subconscious goals are extremely important.
It’s best if their flaw is not such a problem in their lives at the end of your story as it was in the beginning. In other words, it is best, if your character learns something through what happens in the story that causes him to grow as a human being. It helps if your hero and heroine can be the embodiment of the others worst fear.
Oh, and you’ll need a premise. Many writers begin here instead of with characters.
As far as structure, goes, you need a beginning, an inciting incident, at least three turning points (or big moments), the last of which is the black moment when all seems lost. But it won’t be lost because during the journey of your story, your hero has learned something that produces a vital change in him that enables him to win instead of lose. Then you write the happy ending. What the hero learns has to do with the theme of your story.
Many writers write a synopsis before they begin the actual novel. Write your story in present tense in five to twenty pages, depending on the length of your novel. Next write the first chapters. Do not be horrified if the writing is inferior. All first drafts disappoint. But at some point, something magic should happen. The characters start talking and changing all your well-made plans. What they do and say totally confuses you. Keep writing. Adjust your synopsis.
Think of this as play. Don’t listen to negative voices saying you can’t, especially if one or more of them is your own negative self-doubting critic who is trying to destroy you. Personally I have a head full of demons that spend lots of energy trying to cripple me.
Write. When all else fails, write. Surround yourself with positive people who believe in your dreams, and they will have a better change of coming true.