Sure, I'm no expert on these things, but I have been reading a lot and watching all the videos etc about the game. I'm also working on the SteemMonsters Wiki, which was started by @carn. Basically, you need multiple cards of the same name in order to level them by combining them together (something you can't really do with physical cards, haha). The sets are divided into colours, also known as elements, or Splinters in the lore of the game. The colours are green, blue, red, black, white, and gold. Beyond that there are the four "rarity levels" as well, being common, rare, epic, and legendary. Also, there are the two "classes", being monsters and summoners.

So if I say that I have a Level 4 Rare Azmarian Medusa  card, then I will know that this blue Rare monster has been combined with 14 other Medusa's to make it a Level 4 card. Does that make sense? Oh, one thing I forgot to mention is the "finish" of the cards, which is either "Regular" or "Gold Foil" (GF), and the latter will only be able to fight in battles and tournaments with other "Gold Foil" cards, and vice versa. The GF tournaments, presumably, will be where the big prizemoney can be made in the game.