One more question
I got 12 confirmations. Is that all, Or I'd need more?
Is it 1 confirmation for each BTC transacted?
like If I am to receive 100 BTCs I'll need 100+ confirmations?
It depends on your confidence in that transaction.
If you know that it's real and not some kind of fraud, then you may spend it just after the first confirmation.
If you want to be sure - you may need to wait for 2-6 confirmations before doing something like shipping a package to your buyer.