Fly fishing gear is distinguished from other types of angling equipment by the weight of its line. Rather than simply serve as your connection to the fish, these lines are designed with casting in mind. Most fly lines are thicker at the end to improve turn-over and casting characteristics. Always match your line weight to that of your rod and reel.
A leader tapers down in diameter as you move from the point of attachment at the line down to the tippet. The thicker the tippet, the higher the leader strength and the more weight it can handle. So, the bigger the fish, the larger the tippet you'll need. Most leaders are 7.5-9ft long but length can vary.
There are two types of materials used for leaders-nylon monofilament and fluorocarbon. Fluorocarbon is more abrasion-resistant, it sinks faster due to its high density, and it's harder for fish to see in the water. Nylon monofilament is less abrasion-resistant and more prone to float, but it's also less expensive than fluoro line.