I hope someone can answer this for me. I understand how to set up my deck and how to draw new cards during battle. What I don't understand is that sometimes my cards in my deck are shaded out grey and I can't click on them to use them. Is it something I did wrong?
Most likely, you do not have enough Pips to cast the spell. Pips appear at your feet during a duel. If you have three white pips you can cast any three pip spell.
If you have a Gold Pip, called a Power Pip, that counts as TWO Pips towards spells in your main school of focus.