Each author writes differently. Some write by the seat of their pants and put down whatever comes to mind; others plan out every inch of their stories in outlines so detailed they're practically already the manuscript. But no matter what you do, you'll have to hear the characters so you can tell their story.
As for me, I hear two versions of the characters.
One version sits on my desk or shoulder and tells me everything about them, their motivations, etc. If this version doesn't talk to me or withholds information, I get writer's block. Also, if I try to make a character act against some core element that they have, even unbeknownst to me, it doesn't work.
The second version is the one that appears in the actual manuscript and the story. It's the version that the reading audience gets to hear.
How do you hear your characters?