It's called 'floor-loading'.
Each row of pax (passengers) has a single cargo strap (ratchet strap) across their laps going from one side to the other of the cargo bay to use as a 'seat belt'.
A row of pax leans up against the legs of the pax behind them, so their legs act as back support
After 2 hours, most people suffer 'pins and needles legs' so it is very difficult to stand and walk if they have to exit the aircraft quickly
This method is used only in emergencies & requires high-level approval due to the lack of safety measures
Hope this helps