A:
Line weight
Fly fishing line weight is ranked from 1 to 15, with 1 being the lightest and 15 the heaviest
Lighter lines are suited for delicate presentations and for casting light flies
Heavier lines are best for casting large, wind-resistant and heavy flies
Line weight is the easiest to select since this should be matched to your rod and reel
Fly fishing requires a balanced system so match the reel and rod. If you don't, you will hurt your casting accuracy and efficiency.
A 5 weight reel matches up with a 5 weight rod, so it follows that you should select a 5 weight line
Some manufacturers give a leeway by saying you can go one above or below this, say a 4 weight or 6 weight line with a 5 weight reel and rod. If you want to be safe, though, match the line, rod and reel exactly.
Your fly fishing line weight should also be selected based on the fish you want to catch
You'll need line weights from 1 to 7 lbs for lighter fish such as panfish and most trout
Bass need a little heavier weight, from 7 to 9 lbs
Larger freshwater and saltwater fish take the heaviest lines--an 8 to 15 lbs