Others have said it
To furl (roll up) the sail, you pull on the furling line which unwinds from the drum, which turns the drum to wind the sail up. To keep it from releasing and letting the sail back out, you cleat it and then coil the tailend.
When you want to release the sail, you uncleat the furling line, uncoil the tailing end and pull on the leeward genoa/jib sheet to unfurl the sail.
When I furl my sail, I roll it up so that the sheets wrap several times around the sail. This keeps the clew from catching wind and potentially unrolling the sail if I forgot to cleat the furling line. My sheets are loose and the untensioned tail ends wrapped around a cleat or winch drum to keep them from flailing all over the place in a storm.
If I am away from the boat for a long time or there is a good storm coming, I'll tie the clew snug around the furled sail with sail tie or wrap the spin halyard around the length of the furled sail (around the forestay) to keep it from unraveling just in cast the furling line cleat or line itslef fails.
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