If you want a simple deck, then pick a random element, say Water, change your mark to that element (which is Water) buy 15 (Water) Pillars and at least 4 (Ice) Dragons, then buy 11 more random (Water) cards such as Freeze, Toadfish, Ice Shield, etc. You should now have a mediocre 30-card deck!
Disclaimer: Results may vary. I may be slightly biased towards one element. I am not responsible for any losses you incur through this process.
Of course, the deck is far from perfect, but it does get you a feel of the game. There are plenty of guides on these forums, although you should note that most of the knowledge comes from experience. Don't be afraid to pop into
chat once in a while, and enjoy your stay.