Consider the scenario, your domain example1.com pointing to old server and you want to check whether the domain is loading from the new server. Assume your new server IP is xxx.xx.xx.xxx. You can add below entry in your local system hosts file to point website to the new server
xxx.xx.xx.xxx example1.com
File names in various OS
Linux: /etc/hosts
Windows: C:\Windows\System32\drivers\etc\
Mac: /private/etc/hosts
