What is tone/mood in writing?

Tone is more than just the setting, a stormy night verses a sunny beach. Tone is the words you choose to use. Those words change the tone/mood of the section you are writing. During a scary scene, you want to use words that create that tone, blood, crunch, stab, etc. His eyes stabbed into the demonic darkness.

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Here is an example of what I mean.

She entered the elephants' graveyard, fog snaking around her red shoes. Tall rib bones curved up to her shoulders, as she walked around stained bones that protruded from dry, cracked earth. Nothing but the scraps of Death remained in that place. Now read that same paragraph without well selected words. She entered the elephants' graveyard, fog swirling around her red shoes. Tall rib bones curved up to her shoulders, as she walked around dirty bones that shot up from cracked earth. Nothing but the scraps of Death remained in that place.

Just a few words were changed, and it loses tone in the process. But also, the details you choose to write makes a difference. Imagine if I hadn't mentioned the fog, rib bones, or the cracked earth.

Look at the difference between the following.

Partly hidden in the shadows, the man stared at her from across the street. The tall thin man stood next to a broken-down Honda, as the wind ruffled his trench coat, yet Heather couldn't feel the wind. She paused and her hands shook.

The thin man stood across the street, towering next to a rusted Honda that looked corroded and dead. Though he was partly consumed by the shadows, Heather could see his trench coat rippling with the wind, as if he were a living shadow. Yet she couldn't feel the wind. His silvery eyes stabbed at her through the darkness. She froze, her hands quivering by her sides.

The details you choose, the words you choose, and the order in which you write the information all adds to tone.