Catan looks chaotic on your first play, but the underlying game is shockingly simple: build roads and settlements, collect resources when their numbers are rolled, and reach 10 victory points before anyone else.
The most important decision happens in the very first round — your opening settlement placements. Aim for hexes with the highest pip counts (the little dots under each number). Numbers 6 and 8 produce most often; 2 and 12 are traps. Diversify across at least four resource types so you can build anything.
Trading is where new players lose the game without realising it. Refusing every trade because "they'll get ahead" is the single biggest beginner mistake — if both players gain from the trade, you've still gotten value. Trade aggressively early, then tighten up as someone approaches 8 points.
Finally: keep an eye on the robber. Whoever rolls a 7 chooses where it goes, and a well-placed robber on your best hex can stall you for three turns. Build a fallback economy so a single bad placement doesn't end your game.