As far as which end to attach to the backing, the end of the fly line on top of the spool (the first part to come off the plastic spool) is the rear of the fly line-- that way you can attach it to the backing and as you wind it onto the reel you'll end up with the front of the fly line on top of the reel. Put a pencil or something into the center of the spool as an axle so you can wind the fly line onto the reel from the plastic spool as it revolves like a wheel around the pencil -- (The reel and the plastic spool should be lined up in parallel to each other like an old fashioned reel to reel tape player. ) This way you can put the fly line on the reel without twisting the fly line.
As you wind the fly line onto the spool you'll see the fly line is mostly level at the rear until you get towards the front end, where it will start to get thicker-- this is the weight forward part of the weight forward taper fly line.
Here's a helpful link for the the knots you'll need: Fishing Knots | How to Tie Fishing Knots | Animated Fishing Knots
To attach the backing to the reel use an Arbor Knot
backing to rear end of fly line - Albright knot
Leader to front of fly line- Albright knot
( or you can attach the leader butt to that stream lined loop)
Leaders can be pretty basic for saltwater if you don't want to buy them -- To start, for a 9' leader for your 10 weight you might use about 5 feet of 50 pound Ande monofilament blood knotted
to 2 feet of 30 lb blood knotted
to 2 feet of 20 or 16 lb mono improved clinch
or Duncan Loop
You should be able to purchase several yards of clear 50 and 30 yard Ande Premium mono from any bait and tackle shop (not just fly fishing shops) and a 1/4 spool ( about 600 yards) of clear Ande 20 lb for $10.99, or if you can find a shop has them, Ande also sells 50 yard skeins of monofilament leader material on "wristlets" (handy for storage). This is a bit stiffer and more abrasion resistant than the Ande premium mono (regular fishing line). The 50 yard skeins are approximately $6 for 50 lb, $5 for 30lb and $4 for 20 lb test.
You can purchase tapered knotless saltwater leaders, but making your own is a lot less expensive and the basic leaders are pretty simple. After awhile you'll want to learn some more complicated knots like the Bimini twist etc, but for now simple leaders should be fine for redfish, weakfish (sea trout) and snook.