If you're a sailboat racer, or what to become one, you need to become familiar with the Racing Rules of Sailing. Here are some references to help you learn. Note that the rules are updated every 4 years; new version came out in 2021
Links and Resources:
Flags are used for signaling during racing.
Here are some common flags used by the Race Committee to communicate with the boats racing, or about to race. If you are a beginning racer, these are the first flags you'll want to learn. Thanks to UGA Sailing for this fun, informative video!
2nd horn blast and "X" flag (described in video above) hoisted on the committee boat indicate one or more boats (perhaps not shown) are over start line early (OCS)
"Jimmy shut us out!"
America's Cup: Spithill 'hooks' Team New Zealand
Animation of mark rounding and overlaps at the zone. Prada Cup
"Kinetics" means propelling a sailboat by pumping the sails, rocking and 'ooching' the boat with your body. Generally forbidden or limited by the Race Rules of Sailing #42, but allowed in the 470 class in winds over 8 knots. So... an excellent illustration of what it can look like.