If you have read and learned the first three lessons here then you already know the basics. Congratulations! All the rest is frippery. Now you have the rest of your life to wallow in the minutae.
The sails catch the wind (duh). You could argue ad infinitum about the proper shape. Sailors are forever tweaking the sails when underway to try and get the most power out of them. Enough about that.
Nowadays, almost all sails are triangular in shape. Each corner of the sail has a name:
Clew- the other one
Also, each side of the sail triangle has a name
Luff -leading edge
Leech- trailing edge
You have to learn these names. Otherwise you won’t be able to communicate well with your crew members when underway, and mayhem will ensue.
you need to crank down on that thing there so that the thing isn’t flapping and causing that thing to come unhooked from the thing…
also helpful to know the ropes-
halyard- hoists the sail
sheets- control the sail
outhaul- stretches the foot of the sail
lazy jacks- lines that keep the sail in an orderly bunch when you drop the sail
topping lift- a line that holds the boom up off the deck