How to check if confirmation is done or not yet? After sending Bitcoin to any address, how can I check if the transaction has at least one confirmation? 

Should I poll the transaction repeatedly or is there any event when confirmation is  made.
In order to see if the transaction has confirmed, you can search for it in any indexed transaction database. This can include Bitcoin Core running in -txindex mode, or a block explorer such as live.blockcypher.com or blockchain.info, for example. As soon as the transaction has been included in a block, it has 1 confirmation. If it is not found, or is still in the mempool, then it has either not propagated (failed validation checks), or has yet to be mined.