Fly rods come in a range of weights from a one all the way up to a fifteen weight. The smaller the number, the smaller the rod and in turn the smaller fish you will be seeking out. If you wanted to catch a four-ounce sunfish you would want a three weight or smaller. If it was a marlin you are after a fourteen or fifteen weight would be more appropriate. Most trout rods are in the four to six weight range depending upon the size of the river and size of trout lurking within its depths. 8wt rods are great for Pike, Steelhead and Carp just to name a few. There are other factors besides fish size that you may want to factor in as well. If it's going to be a windy day you may opt for one rod weight higher than normal to combat the stiff breeze. If you are throwing huge flies on the end of your line a larger rod will assist you better. Fly anglers tend to build up a “quiver” of rods for various applications over time.
Fly reels also come in weights which correspond with the weight of the rod you've chosen. If you bought a five weight rod you would want to match it with a five weight reel. In fly fishing, reels basically function as a mechanism to hold the line. The actual reeling of line is a function is rarely used. The bigger the fish you are seeking, the more important to have a good drag system. Poor drag systems can cause loss of fish. The drag system is not as important with smaller fish, as YOU become the drag system. Saltwater situations require much better drag systems and quality of reels due to the salt and strength of these fish.
You guessed it, as with rods and reels the line also comes in weights from one to fifteen. Again, if you bought a five weight rod and a five weight reel you probably are going to be looking for a five weight line. There are some anglers who prefer to put a six weight line on a five weight rod, generally this is desired if the rod is a fast action or stiffer rod. Lining up, as this is called, can improve the performance of a stiffer fly rod. The second consideration is the line type. There are three types of fly lines: floating, sinking and sink tip. Floating line is the most common used line type in fly fishing. It is generally a bright green, yellow or orange colored line to which you attach a leader and a dry fly. Dry flies float on the surface of the water (keeping them dry, hence the name), therefore the line needs to float as well. Nymphing is another popular method of fly fishing that uses floating line. Sinking line is used when you are fishing underneath the water. Sinking tip line is used if you are fishing underneath the water with a fly that imitates a baitfish, usually called a streamer.
With leaders you want a leader that will withstand the size of fish you plan to fight. Leaders start at 0X, being the strongest and ending at 7X being the lightest. A 0X leader would be great for a large ten to fifteen pound salmon, and a 4X or 5X leader would be great for a two or three pound trout. If the fish are really picky you may use a 5X or 6X leader so they have less of a chance of seeing the line. As the number gets higher, the smaller in diameter the line becomes. On a really tricky spring creek where the water is crystal clear and the fish are very picky you may use a 6X or 7X leader to fool the fish, even if they are bigger prey. If you are fishing for fish with very sharp teeth such as a muskie or pike you may want a section of steel leader in order to keep the line from being cut by teeth.
The type of fish you are after, and time of year dictates what type of fly you are using. For example, in the winter trout are mostly after midges, tiny aquatic creatures that live in the river system in the winter and hatch into flies barely discernable by the naked eye. In mid to late summer trout can be looking for grasshoppers on the surface of the water, or small baitfish underneath. Muskies on the other hand eat large fish, therefore you would fish with a fly that would resemble a much larger baitfish. Muskie flies can be up to up to 15 inches in length, while a trout fly can be as small as a pencil eraser. There are thousands of kinds of flies out there but depending on the fish you are after you can narrow it down to two or three flies that will always work well.
Fly fishing can seem overwhelming to someone who is just trying to get into the sport. It may seem like there are endless amounts of items you need to purchase in order to get up and running when in fact just the opposite is true. All you really need is a rod, reel, line and a fly to tie on the end and you can be up and running.