The "slope" means how far you rise when you travel 1 unit horizontally. "Steeper" means you rise higher for each horizontal distance ... more slope. A slope of 1/12 means 12 horizontal units raise you one unit higher. 12 horizontal inches raise you 1 inch higher. 1 horizontal foot raises you 1 inch higher. 12 horizontal feet raises you 1 foot higher.
In order to rise 2 feet, you'd have to cover (2 x 12) = 24 horizontal feet on a 1/12 slope.