Ramps are on the back row of blocks.
The Ramp is an angled block released in update 1.8 that is used to walk up inclines on a smooth surface. Ramps work very similarly to stairs do with the exception of the player being constantly moving slightly upwards while walking upwards. Ramps take up a block of space, and shaped as a 45-45 right trianglular prism.
When placed, the slant will be faced toward the player similar to the way stairs are placed.
The different textures of ramps and other blocks.