How to Fishing
You can learn fishing after you unlock your restaurant, from an orc at the docks.
Only E to move the bar. The bar moves to the right automatically while not pressing anything, and moves to the left when you hold E.
For controllers: just hit A (which moves the arrow forward) and get the arrow into the blue area. When it goes left (which is the fish trying to escape) you just let go and the arrow moves back to the left.
Seaweed can be used to catch crabs but its easier to just grab crabs by hand.
Crabs, by extension, can be used to catch Fire Goldfish (and rarely other fish)
Later on, you’ll get more baits that can be used to get even better fish!