In order to fish with a float rod, you have to equip all parts of the tackle (rod, hook, line, reel and bait).
Not all rods can be used at every fishery. On some fisheries, you can use only a spin rod or sea rod.
In some cases you have to buy a given bait to catch a specific fish otherwise fish won't bite. You can find information about baits for certain fish in a fish summary.
If your line breaks and the fish gets away, you get a chance to keep fishing for the price of 3 banknotes.