Once casted, a fishing net will be thrown forward (facing of the fisherman), from 200 range towards a maximum of 1000 range. The net will keep moving for a tick of 200 range, until you stop it, by selecting the fishing area of your will, by hitting "Esc". In order for the fishing area to be selected, your fisherman must be selected. Obstacles, areas with no water and issuing the fisherman to do another command will abort the act of fishing.
Fishing to deep areas will give you a chance of retrieving an item of A/B/C grade with lower chances for the prior grades and higher to the latter ones. There is also a chance of finding nothing. Fishing to shallow areas will always provide you with a gold bonus.
If the fisherman is not given a selected point to fish at (by hitting Esc), he will by default start fishing at the range of 1000 (which is the limit range of the fishing action).
Before the net lands, you can still issue the fisherman to face another point, in case you changed your mind, but make sure the new point is a valid point, that fits the particularities of this system.