Answer:
There are a huge number of fly fishing lines out there, but for the most part they will fall into four categories:
- Floating
- Sink Tip
- Sinking
- Intermediate
Each line is used for different situations, floating lines float on the water and have a monofilament leader attached to the end of it which has your flies attached to it. "Flies," where it is legal to fish more than one fly. When dry fly fishing, a floating line is almost always used, and the leader is "greased" and the fly will often have a floatation chemical rubbed into it to keep it floating. However, even when using floating lines, one can still use flies that are fished below the surface.
A sinking line completely sinks in the water, it has a higher density and is used for what is commonly referred to as wet lining.
Check out the related links for more details on the different type of fly lines