To avoid having to repeatedly scan the entire blockchain, you'd probably be better off scanning it once and building a database table with the complete UTXO set. Then you'd want to use blocknotify to update your UTXO table everytime a new block is created. That way you could just query your UTXO table to find address balances.
Um...where can I input the address that i'm interested in?
I'm not sure what you're asking.
If you are asking how you can add an address to the bitcoin daemon, then you need to have the private key. You can then issue the importprivkey command and the daemon will add the private key to its own list of private keys and calculate the bitcoin address.