nslookup is a network administration command-line tool available in many computer operating systems for querying (checking) the Domain Name System to obtain domain name or IP address mapping, or other DNS records. The name “nslookup” means “name server lookup”.
Wikipedia
Open CMD or Powershell (See How to Open Command Prompt)
Type in: NSlookup
For more details refer to this link: http://www.steves-internet-guide.com/using-nslookup/