How do you write a novel?

It's a stupid question, but a genuine one. How do you write a novel? I have a shit ton of stories I'd love to tell and I've tried on several occasions to put them on paper, but I can never meet the required word count without losing stamina hardly even midway through. The most words I've ever gotten down before losing my drive to continue completely is a little over 13,000.

I have no idea if anyone's going to be able to help me with this, but it's worth a shot, I suppose. Any advice would be greatly appreciated.