In Animal Crossing, the common currency used is Bells. Not bells that you ring, but coins. They come in 100 bell coins, and are used for all purchases in the game. Good ways to make bells, are the Stalk Market, Foreign Fruit, Fishing, Bug-Catching, etc. These small, but very precious coins, can also be stored in bags of thousands and tens thousands. A single bag has the capacity of 99,999 bells which is also the limit to how much you can hold at one time in your pocket. Bells can be stored in the ABD found in the Town Hall. The limit in there is 99,999,999 bells. If you haven't yet reached the maximum, and you've stored your bells in there for quite some time, you'll recieve mail saying that you've received profit, an additional price for depositing for so long.
The best money generating methods are dependent on what you have. If it is an abundance of time, then foreign fruit gathering. If it is an ability to dedicate a small amount of time every day to playing the game, then the stalk market. An eye and memory for what bug or fish to get, then the tiniest of river fish possible, ocean fish and bell crickets are a good basis to start with. If the majority of your playtime is when Tom Nook's store is closed and you do not wish to time travel, then you will need to stockpile valuable things in both your house and on yourself and replace lower value things with higher value things as you find them and sell them in one big go when you are able to.
Now you might wonder what is the best if you simply don't care about the above choices are. I will say foreign fruit gathering. You can haul off 5000 bells worth of fruit if you fill your inventory with them and only carry a slingshot around. Now you might think, that is only 5000 I want to catch three 2000 fish and that will be better. Now see here the thing is that you can gather that batch of 5000 bells fruit a lot quicker than you can catch those three expensive fish. If you place the fruit trees near Tom Nook's you can even cut down on the travel time to sell also. But the problem with relying solely on gathering those fruit is that the fruit takes a while to grow back. And what if on your way from hauling back your coconuts located across the map from Nook's store, you see a fish that might be worth 2000 bells instead of that 500 bell fruit? Why you could up and drop that coconut and come back for it later instead of being a pure fisherman who saw a good catch on the way to Nook's.
Bells may be used for buying anything within the stores in this game, and are quite essential for a fun game play.
 External Links
Related ThreadsHow to make over 3.5 Million Bell in one hour! - last post by @ Jul 18, 2006
Bell Bloodshed 1 - An Animal Crossing Mafia! -Day Phase 4 - Face to Face - last post by @ Jan 10, 2014
Quick Question For Those Who Enabled Bell Boom. - last post by @ Dec 1, 2013
WELCOME TO BELL BOOM, EUROPE! - last post by @ Apr 22, 2013
What is the largest amount of bells you had? - last post by @ Apr 8, 2012