What is Hosts File?
The hosts file is used to map hostnames (in other words domains) to IP addresses.
Using a hosts file, you can change the IP address that you resolve a given domain name to.
When you transfer a working website to us, you can check how it resolves from our server before updating the DNS in order to make sure there will be no service disruptions.
Once you have confirmed on the accessibility of the website upon changing the host file, you may then point the domain nameserver/ A record to us.