Your heading relative to the wind: close-hauled, beam reach, broad reach, running. No boat sails closer than about 45 degrees to the wind — that sector is the no-go zone, and everything stalls in it.
Almost every decision on board answers one question: where is the wind coming from? Close-hauled you sail as tight to the wind as the boat allows; on a beam reach it comes across the side; on a broad reach it is over your shoulder; running, it is straight behind you. The sector straight upwind is the no-go zone: no boat sails closer than about 45 degrees to the wind, no sail makes drive in there and the boat stops. That is why no course leads straight into the wind; you zig-zag up in tacks instead. The costliest beginner mistake, though, is not picking the wrong heading — it is changing heading without touching the sheet. Bear away and the sail goes out; head up and it comes in. Treat course and trim as two separate jobs and you will sail in lurches while the identical boat alongside just goes.