First of all, make sure you major in fishing. Every big city has coaches. If you don't know where to find the guard, if you still don't know, you can ask me and send you a screenshot. After learning, you need to click "Magic Book"-"Professional"-"Fishing". If you want to use it conveniently in the future, you can bind fishing skills to the shortcut bar, and then click fishing at the water's edge until the hook shakes.