The tools every fly fisherman needs to get started.
Every outfit consists of a few basic components. You need a reel, a rod, line, and a fly. While there are many options for prebuilt setups for beginners, intermediate and advanced level fly fishermen will want their own customized outfit.
Lets break down these individual components.
Reels
The reel is the home for your backing and fly line, and serves as the brakes for that fish when it runs. There are a plethora of companies offering a wide array of amazing reels, it can be hard to decide what to go with. Hopefully this guide can point you to the right features you need to make an informed decision
Drag: Click and Pawl, Unsealed, and Sealed Drag systems
Click and pawl drag systems are your most primitive forms of drag. its simply a sping loaded pawl that drags over a sprocket. the drag is non adjustable and determined by the spring tension. Any additional drag must be manually applied by "palming" the spool. These reels are best suited for smaller trout and panfihs until you can master applying palm pressure to apply appropriate drag to larger trout, bass, or other smaller game fish.
Unsealed drag reels are reels that encorporate a drag system by mashing two carbon or cork disks together. these reels are less expensive than sealed drag reels, and so long as you keep them free of debris and salt, will hold up perfectly fine for just about any fresh water application you can throw at them. The only situation I wouldnt suggest an unsealed drag would be in below freezing temperatures, as water can get in to the drag system and freeze, causing you to break off.
Sealed drag is the best all around system as the drag disks are encased in a waterproof housing, thus preventing dirt, debris, and water from being introduced in to the drag. If you fish saltwater, I would always recommend sealed drag. The sealed drag also significantly reduces the chances of the reel components freezing in the winter time.
Arbor Size
Arbor size refers to the depth of the spool from the outside of the reel.
Large arbor reels are most common, as they provide the best overall line retreival per crank while still offering sufficient backing for most game fish. They have the shallowest spool that will still accomodate a fly line and 100-200 yards of backing. A large arbor reel should be perfectly fit for almost any fresh water application.
Mid arbor reels have a deeper spool compared to large arbor reels, so they can hold more backing than a large arbor spool. These reels are almost exclusively for saltwater game fish that go on long runs, or some two handed rod applications where the fly line is much thicker than a standard fly line.
TL;DR: You wont go wrong with a large arbor reel.
Reel Size
This one is pretty easy, match the reel size with the rod you plan on outfitting. The only exceptions to this are upsizing your reel to balance out a much longer rod, or upsizing based on the fly line thickness. Luckily most fly reels are in a general size grouping (2-4, 4-5, 5-7, 7-9, etc.), which already accomodates that.