Risers are the four webbing straps that run from the shoulders of the harness up to the canopy's suspension lines. They carry the entire load of a jumper under canopy, and they double as a control surface.
Front and rear
Each shoulder has a front riser and a rear riser. Pulling a front riser makes the canopy dive on that side; pulling a rear riser slows and flattens it. Both are used for steering when toggles are unavailable, and front riser input is central to high-performance landings.
The toggles for normal steering are stowed on the rear risers, which is where a jumper reaches to unstow them after opening.
These pages explain what things are so the language makes sense. They are not instruction and cannot substitute for it — skydiving is taught in person by rated instructors at a drop zone, and anything involving equipment handling or emergency procedures belongs there rather than on a web page.