To start, you need to craft a Crawfish Trap. Place it underwater in any swamp, river, or ocean biome. The trap works automatically over time and will slowly collect raw crawfish. You have to put spam, chicken, kelp, bread or any other meat i8n the trap so it works.
There are 5 different color variants you can catch:
You cannot cook these crawfish in a standard furnace or smoker. Instead, you have to boil them using a water cauldron.
Eating raw crawfish isn't very effective (restores only 1 hunger bar). However, once boiled, any of the 5 cooked crawfish variants becomes an excellent food source, restoring 5 full hunger bars (10 hunger points) with high saturation.