To make a deck valid you need 20 cards with the little asterisk at the bottom of a card, 40 normal cards you can only have 4 of the same card and 0-5 LRIGs of the same character pic related these are all LRIG cards they are all named Tama. They evolve into each other. Start from 0 and each turn you can evolve them up to the next level 0->1->2 etc.
http://selector-wixoss.wikia.com/wiki/Selector_infected_WIXOSS_Wiki bunch of info on the cards and various mechanics for example look up double crush and it will explain to you what that does
http://webxoss.com/DeckEditor/SearchTips_en.htmlThis gives you tips on what to search for. For example WD02 would give you a prebuilt deck that you can use as a basis. I believe it currently goes from 1 to 12
There are exceptions to rules here and there like in all card games, but this is basically how it works