Here are the basics on how to catch fish.

Starting off, there are four different types of fish.

Fish- The most common type of fish, it can be eaten to regain some food bars, used to tame ocelots, and be cooked in a furnace.

Salmon- Salmon is rarer than regular fish, it has the same properties as regular fish.

Pufferfish- Pufferfish are uncommon, with about a 25% rate of finding one. They are poisonous to eat, and can be used to make water breathing potions.

Clownfish- Clownfish are very rare, with a 2% rate of finding one. They can be used to tame ocelots, and be eaten (Though this is not very cost efficient)

The best type of fishing hole is a 2x2x6 pit. Make an infinite water source, then create a pillar 6 blocks up, and fish from the pillar.

This is a table from the wiki that shows percentages of catching items.
Fishing Rod - Minecraft Wiki

Lure increases fish rate, and Luck of the Sea increases treasure rate. Fish is an easily obtainable source of food, and when cooked, can be used as an alternative to steak.

The average wait is 5-45 seconds, the calculations are also on the wiki.

 

Moved thread to "guides and how to"

 

Thanks!

 

Add something in about fishing with nodus. It's allowed and makes fishing easier.

 

I am not going to, as most users do not hack and using nodus to make it easier is not legitimate.

 

Using nodus is legitimate... http://www.skyblock.net/threads/acceptable-hacks.11728/
As you can see, autofish is allowed.

 

I guess technically it is, but I don't think many players will use nodus to fish...

 

This post is glubly. It reeled me in with its detailed explanations. Definitely a good catch.