From playing the GBA game :
1. when I put a card in my "mana zone" does that mean I cannot ever use if for that fight?
Yes, unless there is some other effect from cards that would move it from the mana zone.
2. is there an advantage to putting one card or another (of the same color) into the mana pile? I mean if both a 5000 strength blocker and a 1000 point spell put in the same amount of mana why would I ever put in the expensive cards?
I'd say it's more of a strategy thing. If you draw a lot of high cost cards in the early game, it may not hurt you to put a couple of them into the mana zone since they won't be helping you out much at that time. Early on, I'll usually try to lay out a couple of cheaper creatures to gain board advantage, but I try to keep at least one big creature in my hand to deal with any big opponent threats later on.
3. Can someone explain battles a bit? Last night for example I had three monsters summoned but I never got the opportunity to attack. Then suddenly I could....I think I can only attack if one of the enemy monsters is already tapped but I am not sure. So any insight would be great.
You are correct in that you may attack an opponents monsters directly only if they are tapped. Otherwise you can attack a shield or the opponent (if no shields). Let's see...a couple other things :
- You can only attack the turn after you summon a creature.
- You can only block if you have a monster with the abiltiy "blocker"