Fishing is good for reliably obtaining fish meat.
What you need
At minimum you need some worms and a fishing rod. Recommended additions are fisherman's jacket, a shovel and a good spot to throw your lure.
To start fishing equip your fishing rod, (also the jacket for better results) approach a tile of deep water and hit action once (do not repeat). You need to have worm to be used as a bait. This will cause you to throw the lure.
From this point on you need to wait a certain amount of time until "A bite!" appears in your message log. If you prefer observing the map an exclamation mark will appear briefly over your spot of water. When this happens quicky hit action, to get the fish out of water. Your worm has been devoured. If you hit action fast enough you will be rewarded with meat and experience. Otherwise a message "It got away..." is given and you are now poorer by one worm.
If you use action during fishing your waiting for fish timer is reset thus there is little benefit in doing so. Walking away from your spot or changing facing cancels your activity.
Hey, I got a fish!
Congratulations. Amount of fish meat pieces gained is governed by formula (W+1) / 2 rounded down where W is weight of caught fish in lb. Game informs you how heavy was your catch in message log. Thus you gain one meat piece for 1-2lb fish, two pieces for 3-4lb fish, three for 5-6 lb fish and so on.
Unconfirmed: the weight of caught fish seems to be between one and your fishing skill.
Experience gained is linearly proportional to weight of your catch. You receive base of fifteen points per 1 lb of fish weight.
How to find good fishing spot
The time you have to wait until a fish catches the bait varies greatly depending on where you throw your lure. Mystera Legacy determines location something called 'the sweet spot' for Galebrook. Some coordinates is chosen randomly and they persist for a period of time. Whenever you fish the distance to that sweet spot is computed and it is a major factor in how long you need to wait until something bites. When you have been waiting for a full minute just forget it and walk a significant distance to another body of water. A hundred squares or more is recommended. After you catch something you may be given a hint. Usually it will be of the form "You suspect more fish to the <world direction>". Despite it says suspect the hint never lies and is precise. Follow the direction and try fishing in that part of the world, using further information to track down the sweet spot before it is moved again. If you receive "There is a lot of fish here" stay and enjoy your day. Until the sweet spot is moved to another random place fish will catch here very fast, allowing tor good experience gains and plentiful meat. Note that the spot chosen does not need to be a deep water square. It does not need to be anywhere close to any water for that matter. This is why you need a shovel for best effects. When you walk sufficiently far to try another fishing attempt and there is no water in sight start digging until you uncover an underground spring. Training digging prior to looking for sweet spot may come handy.