Client PC automatically get an IP address from the scope specified in the DHCP server.

DNS works as a interpreter for computer.Computer doesnot know the alphabet so if you type google.co.in ,machine could not understand what is google.co.in so DNS convert it into IP address.thats called A record or forward lookup zone.DNS also work as PTR record.where if you give ip adderess you will get the name.thats call reverse lookup or PTR record or pointer record.