I've heard a lot of people say that they'd like to write a novel, as every other writer probably has. Go for it! Let your story unfold. Let your imagination overwhelm you. Put your fingers to your keyboard and let 'er rip!
Then the next thing you need to do is learn the skill. Join a writers' critique group. Leave your ego at the door, because you're going to be skewered on a regular basis. What you see as a masterpiece seldom is at first.
When your manuscript is honed and polished. It can be submitted to Publishing Houses, agents, editors, or even be self-published. First hand experience says that unless you're fortunate, you're going to have a drawer full of rejection letters before you are accepted by someone.
After you are accepted, it can take up to a year or better to actually become published, and longer than that to receive your first royalty check, so don't quit your day job.
Be serious about writing. Decide whether you love it for the recreation and creativity or for a career. There's always room for more good writers!