Backing is what you put on before you attach your fly line to your reel. Backing is often 20 or 30 pound braided Dacron that is in place in case a large fish takes all of your fly line. Be sure to attach this to the reel using the arbor knot and then tie the fly line to the backing with a Albright knot.
Leader and tippet choices all depend on the type of fishing youíre doing. Size is shown as 0X, 1X, 2X, 3X, 4X, etc. The higher the number, the smaller the diameter of the tippet. If youíre targeting trout and other small to medium sized fish, youíll only need a 5X leader. This is thick enough to withstand any headshakes or runs that fish this size might give you. The leader is what you attach directly to your fly line using a nail knot.
For tippet, smaller diameter is better for fooling fish because it is harder for them to see. The smaller diameter is not as strong so you have to balance strength and stealth. Tippet should be the same size or a size smaller size than your leader. For example, if you have 5x leader, use 5x or 6x tippet . 5X leader and tippet is light enough that the spooky trout wonít see it and strong enough that youíll be able to handle some larger fish. Youíll attach the tippet to the leader with a double surgeonís knot.