You'll want to take a look at page 16 in the rulebook.

1. Looks (i.e. art) is completely irrelevant. Unless it says x army only or Order/Destruction only, you can use it in any army

2. You select your command cards as a party of army construction.

Hi PanKalich! Welcome to the best 2 dimensional wargame out there.

Dkartzinel is right on. But you should know, the expectation in this game is that everyone has their own set. What that means is that you should be able to take any card you want as long as your army meets the requirements. i.e.: an orc army may take generic, destruction, and orc only cards, but not an order, or high elf card. Their is no draw or selection process, you just pick the ones you want, up to the limit provided by your generals.

The problem with this is that if you are using one set for both players it means you both can't have eager troops, a very popular generic card, unless you have multiple copies of the set.

To counter this, I highly recommend using proxies, until you get a feel for the game, and decide if you like it or not. Once you've been playing for a bit, you may want a second core set. Or, your opponents may buy their own sets, which will eliminate the problem.

Second core sets are actually a pretty good investment, there is very little waste in the box. The only disks you might question needing extra copies of are the generals, and even they have use, should you and your opponent wish to run a mirror match. i.e. orcs v. orcs.

Anyway, hope this helps! Good luck, and have fun.

Oh! one last thing, there is a blog: https://snipertroll.wordpress.com/ which is awesome, and will answer tons of questions you might have, as well as providing sample army lists, and discussion about some of the strategy behind Diskwars. Also, you might check out the Board Game Geek page for the game as well. Lots and lots of info on those two pages.

Thank you both for explanations and tips.