If it takes 6 blockchain confirmations to confirm a transaction to the network and each confirmation is about 10 minutes, how come sometimes When I recieve bitcoin it came faster like 30 min or less?
A transaction is confirmed once it has been included into a block.
Each subsequent block adds 1 confirmation to that transaction. A bitcoin transaction is considered to be
completely irreversible after 6 confirmations.
If you are dealing with lots of money, wait for 6 confirmations. For standard transactions or transactions with a lower amount (less than a few thousands), 1-3 confirmations are absolutely fine.
Regarding your second question.. the target (and therefore the difficulty) is chosen so that on average(!) there is a block each 10 minutes.
It is very well possible that we have 3 blocks within 10 minutes, or 2 blocks withon 60 minutes. After all it is pretty random, but the average will be ~10 minutes.
