A cutaway is the release of the main canopy from the harness, using the three-ring release. It exists so that a malfunctioning main can be got out of the way before the reserve is deployed into the space it occupied.
Why release rather than just deploy the reserve
Deploying a reserve into a partially inflated or tangled main risks the two canopies interfering with each other. Releasing the main first gives the reserve clean air.
The three-ring release makes this physically easy regardless of load, and the decision altitude at which a jumper commits to it is part of their training.
The freebag and finding gear afterwards
A cutaway main falls separately and has to be recovered, which is why many jumpers fit an RSL or MARD — devices linking main release to reserve deployment — and why reserve freebags often carry contact details.
As with malfunctions, the procedure itself belongs in training rather than here.
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.