Well, first you need to get a fishing rod (old rod, good rod, super rod) and go to a body of water (lake, ocean, dock). Then when your standing in front of the water, go to the Key Items pocket of your bag and bring out your fishing rod. once it says "Oh, a bite" , press the A button right away. If you press it too late, the fish will have gotten away. Hope you can fish now. P.S. To get the old rod talk to the fisherman near the dewford gym, to get the good rod talk to the fisherman on route 118, and to get the super rod talk to the fisherman in the house north of the space center.
old rod is in dewford town, great rod is on route 119, and super rod is found in slateport town, in the pokemon fan club building.
You find old rod at dewford town You find Good rod at route 118 You find Super rod At Mossdeep town in a building. (Hardest to find)
You get the fishing rod at your home after the elite four.
one of the fisherman on route 32 will give you a fishing rod.
Lilycove city, while fishing with a super rod.
In route 119 by super rod fishing.
go fishing in falador town with a good rod of super rod or surf.
go to route 118 and talk to the fishing guru there
Gyardos is in Pokemon emerald and leaf green/fire red in emerald you can find him in sootopolis city by fishing with the super rod
old rod is in dewford town, great rod is on route 119, and super rod is found in slateport town, in the pokemon fan club building.
At Dewford town
The Super Rod is the only Rod that you can use to encounter Feebas in Emerald.
You find old rod at dewford town You find Good rod at route 118 You find Super rod At Mossdeep town in a building. (Hardest to find)
You can only get a Corsola by trading it from Ruby, Sapphire, or Emerald. You can find Corsola in RSE by fishing in Route 128 (super rod), and by fishing at Ever Grande City (super rod)
Feebas appears when fishing with an old rod in route 119 (extreme rare to the max but I got him in pearl).
In Pokemon Emerald Carvanha evolves into Sharpedo at level 30. You can also catch wild Sharpedo in Routes 122 to 133 by fishing with the Super Rod.
you ask a fishing man