I know I need backing, and fly line, but I have just used a short section of monofilament to use as a leader, what should be before my fly line (tippet, leader)?
You can find a lot of good info in the lines, loops and leaders section.
Starting at the fly and working backwards:
Tippet: This is a section of line that you don't want the fish to see. Also, it is the last (or first) link in the chain. The size will depend on the size of fly you're using. For panfishing I generally go with 4x or 5x for flies up to size 10. Bigger flies (i.e. bigger hooks) require more force to get a hookset so I increase the tippet strength accordingly.
Leader: The section of mono or fluro that connects the tippet to the fly line. Usually (not always) tapered to help make a good presentation when casting to specific fish. The idea is to put as much distance between the end of the flyline and the fly so the fish don't hear the line when it touches down on the water or see the thick fly-line before they see the fly. Total length of leader is really goverened by the situation you are in. Generally the longer the better but there are times when a very short leader makes sense. About 7ft would be the minimum I would use with a floating line and preferably something like 9ft. Another old rule-of-thumb" was to keep the leader/tippet total length about the same as the length of the rod.
You an buy commercially tapered leaders with integral tippet and they work great but can be expensive. I trick I use is to take a commercial tapered leader (say 9ft with a 5x tippet). I snip off the tippet portion (usually the last couple of feet - you can see where the taper begins). Then I make a tiny loop at the thin end of the leader and add tippet from spools as I need it. The tapered portion is very strong and will last a whole season.
Backing: This is usually dacron. For freshwater you don't need anything terribly sophisticated. It serves a couple of purposes. First, it fills out the fly-reel spool to provide a better "arbor" for the fly-line. A tightly coiled fly-line will be difficult to cast and will need a lot of stretching. Second, if you hook a really big fish and it takes off into the next zip code the backing gives you some measure of safety before everything goes tight, at which point something usually breaks. But hey, that's what makes great fishing stories