Here's a quick tutorial on fly tackle:
Fly lines are set up in a three-piece system:
Backing -- which is kinda like thin string. It's purpose is to lengthen the system beyond that of the fly line, and add diameter to the reel's spool, making it easier to retrieve the line. Backing lasts virtually forever.
Fly line -- a plastic coated line that is built with a taper. The most common and best taper for a beginner is a weight-forward taper. This expands slightly towards the tip end (if you put it on correctly), adding weight which makes the cast easier to manage. Fly lines will last quite a while (years), especially if you take good care of it -- keep it clean, keep it off the ground so you don't step on it. The fly line should match the rod's weight -- which will be on the rod.
zhoyt gave a good set of guidelines for line and rod weight and fish type. Rod weights go from 1 to 10 (with some smaller and larger). The practical ranges for fishing for trout, panfish and bass are about 3 to 8. Smaller means lighter tackle, larger number means bigger.
Leader -- a section of monofilament (like regular fishing line) that also is built in a taper, from thick at the butt end to very thin at the 'tippet' end that's tied to the fly. When the tippet end gets too short or tangled up, you can tie a piece of new tippet on. When the whole leader gets messed up, you can replace that. Leaders are sold in length/tippet size combinations like 9-foot 5X.
Tippet sizes range from very fine 8X to pretty stout 1X. Ten minus the tippet number equals the approximate pound rating, i.e 1X is about 9 pound test, 8X is about 2. Practical tippet sizes for trout would be about 4 to 7X, favoring the larger number (smaller size) for small flies in trout parks, larger size for larger flies and/or fast/broken water.
Sing along: The back-ing's connected to the fly-line. The fly line's connected to the tip-pet. The tip-pet's connected to the fly-eye.
Rods range from 6-1/2 to 9-1/2 feet (again, with some shorter or longer). A practical range for most is 8 to 9 feet.
So, about an 8-foot 4 weight with a 9-foot leader tapering to 6X would be a pretty good setup for Bennett Springs, give-take.
Hope this helps.
PS: Cabela's will sell you a package with all this put together.