Buying Supplies Needed for Fishing and Learning Fishing Skills
1.) The first thing you will need to do it head to the closest GM Shop and click "Next Page" then click the "Fishing" section then click "Supplies". Once there you will need to buy a fishing pole for your grade which will likely be the Triton Pole, then buy a good amount of S-Grade Fishing Shots (or whatever grade you need), and lastly buy whichever lure you want to catch what fish you want (Lures help you catch a particular type (ugly, nimble, or fat) of fish. According to their descriptions, green is supposed to catch more nimble, yellow more ugly, and purple more fat. Or Prize Winning Lures give a higher chance to catch a "Prize Winning" fish).
2.) Now that you have the items you need you will need to find the Fishermen's Guild members, They are located in harbors and magic shops in towns, I use Giran Harbor because I know one is there. Once you find one, talk to them and click "Learn fishing skill" and learn/max out all of the fishing skills (except Expand Common Craft, this isn't needed to fish). Now that you have all the supplies and skills needed to fish, you are ready to start fishing.
The Basics of Fishing
Fishing Shots are close to the same as soulshots, they double the damage given to the fish. Although, if you do the incorrect move (reel or pump) to catch the fish, the fishing shot doubles the amount the fish is healed. Spamming these isn't always the best option they mostly should be used for fish that are hard to catch. They also can't be set to auto use like shotshots can.
How to Fish
Fisning is quite easy once you get used to it, it's beneficial for beginners to use beginner lures, they show icons of the skills you need to use which helps with learning to begin with. Find a section of deep water (water that causes the breath meter to show when your in it). Then put the skills you just learned on the hotbar: Fishing, Reeling and Pumping (the order is up to you), also put your Fishing Shots on your hotbar so you can use them easily if needed. Also its smart to put your main weapon and a few skills on the hotbar as well in case you fish up a monster.
Now stand close to the water on the shore facing the water of course, then using the "Fishing Skill" which will cast your line and start the fishing. Once the line is cast you will see a window pop up that shows your bobber, shortly after that it should say "The fish took the bait", a couple of seconds after this a bar will pop up in the window and this is when you will need to start using Reeling or Pumping skills.
There are a couple of ways to figure out which skill to use (Reeling or Pumping). The way most people recommend is to watch the fish hp bar that popped up, If the fish HP bar is not regenerating then use Pumping skill, and if the fish HP bar is regenerating then use Reeling skill. If you do this correctly the fishes HP bar will be going down as it loses HP points, if you are doing it incorrently the fish will instead regain HP. If you get the fishes HP bar down to 0 before the timer runs out, you catch the fish. (After a little practice it will become very easy, Occasionally while fishing you will fish up a monster, just kill it and continue.))
While fishing you have a chance to spawn a Dimensional Portal, if one pops up go into it and complete it for a chance at Armor Tokens and other useful items.
If you double click on fish you've caught you will "open" it, there is a chance of failing to open a fish. Fish can give common craft materials which can be used for recipes or traded for Proof of Catching Fish in the GM Shop or at the NPC you learned the fishing skills at. Once you have saved up some Proof of Catching Fishes you can use them in the GM Shop in the "Fishing" section to get many different cool and useful items. (Note: Making higher level materials is recommended if your trying to get Proof of Catching Fishes, for example 4 Fish Oil = 4 Proof of Catching Fishes can be made into a Greater Fish Oil which is worth 5 Proof of Catching Fishes.)