AP (red-and-white striped pennant) — "Answering Pennant" = we're waiting. Flown ashore it means stay on land, racing is postponed — usually waiting for breeze to fill in. When it drops with a horn, kids launch. This is the flag behind every "when do we come back?" text.
Class flags — each fleet (Opti, ILCA, C420) has its own flag shown during its start sequence. When your kid's class flag goes up, their countdown is running.
X (blue cross on white) — individual recall. Someone was over the start line early. The race committee will try to call out sail numbers; that boat has to circle back and restart.
First Substitute (yellow-and-blue triangle) — general recall. Too many boats were over early to sort out. Everyone in that start comes back and the sequence restarts. Not a disaster — it happens all the time.
N (blue-and-white checkers) — abandonment. The race in progress is cancelled (usually wind died or shifted badly). Boats return to the starting area and wait.
Orange flag — the start/finish line. The line runs from the orange flag on the committee boat to an orange ball in the water. If you're watching for finishes, watch that gap.