Fishing is a useful activity for learning how to do Rune Factory 4. You can acquire a variety of different specimens, and you can start doing this activity relatively early. You receive your first pole by talking to Eliza, who has a request for you from Vishnal. The mailbox also provides a good market to use to get started.
When you receive the cheap pole, press the L button to access your quick access inventory and equip it. You will find it under the farm equipment. When you've equipped it, the most accessible place to find fish is in Selphia: Dragon Lake, which is on the west side of town.
You want to hold button B when you reach the water's edge to bring the pole back, then release it to send it into the water. There are dark shadows of fish in the water, swimming around, and they should notice your hook after a little while. But you don't want to withdraw it immediately. The fish are shy, and they will push it a few times before officially catching it. When they do, press button B again to roll it up and grab it. You will find better, better quality fish when you get top quality rods.
Fish are great for gifts, cooking, or only selling in the market when you need the extra gold. To acquire better fishing rods, you need to eat Porcoline Farming Recipe Bread, which provides you with your first cooktop. Finally, you should receive new fishing rod recipes for the future, when you have a forge.