Welcome, and congrats on the new boat! I love my H18, it's much faster than most other dinghies and keelboats!
Where on the Great Lakes are you? There are a couple of clubs that you should check out and introduce yourself! They can help you figure out how best to rig your H18 as well, and help with the nuances of cat sailing. CRAM (Catamaran Racing Association of Michigan) has sailors all over the states of Michigan & Ohio, CRAW is all over Wisconsin, Fleet 119 near Buffalo, NY (WNY Catamaran Association on facebook), and Fleet 204 in Syracuse, NY. All are pretty active clubs with very inviting members, and all except Fleet 119 race actively. They each have their own websites, but they are also very responsive on facebook.
I had a lot of the same questions my first time! Take a look closely at the assembly manual that Matt linked to, that helps a bunch!
These videos were very helpful for me:
https://www.youtube.com/watch?v=dl7kZOQ5WQkhttps://www.youtube.com/watch?v=_QLltz31cy8To expand a little on Matt's responses:
The jib does pin to the jib furler & forestay adjusting plate at the tack. The lower of the two holes in the furler is for a pin and ring to pin the forestay to the furler, the upper hole is for a shackle to pin the jib tack to the furler. The jib halyard was a bit trickier to understand at first, but it's pretty simple... you run the free end of the forestay down through the shackle holding the tack of the jib to the furler, then up through the sheave at the end of the jib halyard wire, and then back down through the jam cleat on the jib.
The shrouds should be snug enough that your mast doesn't flop from side to side if you rock the boat. The leeward shroud will always be loose when sailing, but if you grab and pull on the trapeze wires in the parking lot/on the beach, the mast shouldn't move much.
Daggers are just jammed against the dagger well by the bungee in order to keep them in place (up or down).
Switch the rudders/tiller arms for the port & stbd rudders. I didn't get it at first, but as matt said the tiller arms on each rudder are bent just slightly inboard. If you get them backwards, your rudders will be toed in quite a bit. I marked mine with red & green vinyl tape so I don't get them backwards ever again. There is a way to adjust the rudders slightly, by loosening a screw and sliding the adjuster at the end of the tiller crossbar in or out, but if the arms are switched, you won't have nearly enough adjustment.