Nets have been used for fishing for many centuries. It takes a fair amount of skill to use one, but it has greater rewards and provides a different variety of catch.
A skilled fisherman can make their own net out of some string and some fishing weights. Weights can be crafted by a smith from any metal and string can be made from any fiber.
Once you have your net, you'll want to 'cast' it. You can simply 'cast net' or 'cast net to the direction' to cast it into a specific body of water. You'll want to remember to hold on to the rope once you've cast it.
Once the net is cast you may 'pull rope' to haul in the net and see what you've caught.
Happy Fishing!
See also: help fishing, help lobster fishing