I have never joined a a tournement before, when you join are cards given to you almost like a sealed deck or draft? Or do you enter with a premade deck. Also What if you have only upgraded versions of weapons you wish to use? Or arctic octopuses or other cards that are more challenging to obtain.
My bad. The cards are achieved in the original game by you, be it by spins or by simply buying them. If you only have upgraded versions of the card you wish to use, you may use them in the upped tournament (3 out of 4 tournaments are un-upped; the fourth one is upped). That means that if you have a lot of upped cards, that could be bad for you in a un-upped tournament, but it would help you in the upped tournament.
You use "PVP duel" to find and fight your opponent, so you won't gain any cards/money/score for the duration of the whole Tournament. Prelims are normally best of 1, with round 1 forward being best of three. Then the top 4 players gain prizes, given out as Redeem Codes.
If you have any more questions, feel free to ask. Tournaments rules always change, though, so be sure you have a legal deck each tournament. Checking the "Tournament Rules" in this same board will probably answer most doubts you have, but if it doesn't, you can always ask.