Originally Posted by cardiacpaul
What it is:
When one loses the ability to turn the boat using the rudder and it rounds up so that it is broadside to the wind and heeled over, usually at an extreme angle, one has broached.
Note that this description is of a "round up" broach, in which the bow heads up into the wind. There is also a "round down" broach, in which the boat jibes and the wind is on the opposite side of the boat with the sails still trimmed to the other side. In big wind, this stops and typically lays the boat down. Normally, a "round down" is worse than a "round up."
Typical advice, I believe, is to release the sheets to recover, but if you have a preventer on it could be harder.
As for learning to fly a spinnaker, isn't it also common to simply keep the main covered and the genoa below deck, and only focus on the spinnaker to begin with?