Anatomy of a simple one-fleet race
Before the Start:
The course consists of a start/finish line and one or more buoys or markers that serve as turning marks.  The start/finish line consists of a line from the anchored committee boat to a nearby buoy or marker.  Boat crews practice moving their boats around the starting line to get a feel for conditions on the course.  The Race Committee hoists flags to announce the course that will be run. A letter flag announces the shape of the course and a number flag tells the direction to the first mark. Shown at left are the “F” or “Foxtrot”, which indicates a simple out-around-a-buoy-and-back course; and a “3” pennant, which says that the buoy is to the west, about at 270 degrees (west). (An Olympic racing circle consists of 8 turning buoys arrange around a central mark, with buoy no. “1” placed to the south, “2” to the southwest, and so on.).
A typical start sequence:  The start is almost always an upwind start; the first mark (buoy, float, “pin”, or other marker) is upwind of the fleet. The direction of the wind, the right-of-way rules, the position of other boats, and other considerations may cause skippers to want to cross the starting line at a particular place.  This might not work so well if several skippers have the same spot in mind! Shortly before the “start sequence” begins, someone on the committee boat sounds a horn to get the fleet’s attention.
Five minutes before the start, the “Class” flag is raised and some crews jockey their boats so they’ll be in the best possible position at the start.  (Most races in New Mexico start as a single class, but big regattas elsewhere could have several classes starting, with start sequences following one right after another.)  A sound signal (horn, gun, etc.) may be made, if possible, every time a class or prep flag is raised or lowered, but the flag is what counts.  On each boat, one or more crew will be keeping careful track of the time to help the skipper arrive at the start line at the start time with the best speed and position relative to other boats.
Four minutes before the start, the “Prep” flag is raised to fly next to the class flag.
A minute before the start, the prep flag is lowered, leaving the class flag flying by itself.
At the start, the class flag is also lowered.
(Sometimes the start is different; for example, a special race flag might be raised at the start of the race.  All the details of how the race is run should be explained at the pre-race skippers’ meeting or in the club’s race instructions.)
The start is clean if all the boats cross the line on or after the gun without getting in each other’s way.  A boat that is over early has to go back and start again, without getting in any other boat’s way.  If a lot of boats are over early, or the race committee makes a big mistake in running the start, a “general recall” may be announced and the race may have to be restarted.  Otherwise, the race is on!
Suppose three boats, “A”, “B”, and “C” have arrived at the start line as the race committee (“R.C.”) lowers the class flag and makes a sound signal at the start.  A is ahead of B on starboard tack near the committee boat; C is on port tack near the pin.
Ooops! Boat A is over the line early and will have to turn around and re-start by crossing the line again. While Boat A is going back to the line, she has no rights, and must give way even to port-tack Boat C.  If Boat A gets in someone’s way she can be protested for fouling.  Because only one boat was over early, the rest of the boats will continue the race.  The committee boat may send a signal to Boat A that she has to re-start.
During the race, boats follow racing rules, which are a special variation of the rules of the road.  A boat that interferes with a boat that has the right of way has fouled the right-of-way boat.  A boat that commits a foul can generally make penalty turns to “atone” for the foul. Otherwise, the boat that fouled could be protested and disqualified from the race.  Because the first buoy is normally upwind of the fleet and boats can’t go straight upwind, boats have to sail at an angle to “tack” to the mark.  Obstacles such as the shoreline and other boats may force them to tack several times.
Tacking requires good timing and teamwork; a bad tack could cost lost momentum, time, and position versus the other boats.  If the wind isn’t blowing straight from the mark to the start line, tacking in one direction instead of the other may result in a shorter, quicker trip to the mark.  However, the shoreline, patches of lighter or stronger air, “dirty air” behind other boats, shifts in wind direction, obstacles, and the maneuvers of other boats complicate the picture for the racing skipper.  Many of the crews will maneuver to try to catch up with others or to “cover” their rivals to keep them from passing.
The racing rules and regatta rules tell the skipper on which side to pass the buoy.  The object is to turn close around the buoy, without hitting it, losing too much speed, or giving up too much ground to other boats.  The rules say when a boat rounding a mark has to give “buoy room” to other boats and say what has to happen when boats that are still approaching the mark encounter boats that have already made the turn.  (Overtaking boats give way to boats clear ahead; starboard tack is “privileged” over port; and, where two boats are on the same tack, upwind gives way to downwind.)
As the boats round the mark, spectator may see colorful, balloon-like spinnaker sails hoisted on some boats for the downwind run.  The racing strategy continues to be tricky, because a boat that is behind another boat could cast a “shadow” of disturbed air onto a nearby downwind boat and try to pass the downwind boat.  Crews also try to guess which side of the course might have the best wind, and try to pick out a course that will keep them out the way of privileged boats and “dirty air” from upwind boats.
For the simple out-and-back “Foxtrot” course, the race ends as boats cross the line.  However, other races may have two, three, or more turning marks and multiple circuits of the course.  Some races may use marks other than the basic Olympic Circle marks and may have detailed racing instructions that have to be explained to the crews before the race begins.  Most often, a day’s program of racing consists of several races; that way a single bad race isn’t disastrous to a boat’s standings.  Some races are be scored with “throw outs” so a boat’s worst race doesn’t count in the standings.