Parked domains will display the same content (the same website) as your main hosting domain. It's a great feature if you wish to have multiple domains for your website.
To park a domain, go to Websites → Dashboard, search for Parked Domains on the sidebar, and click on it:
Once there, enter your domain (that you wish to park) name and click on Park:
You can also manage all of your parked domains by scrolling down to the Parked Domains section. In there, you can see if the domain is pointing to Hostinger, as well as the option to remove it:
If you had email accounts created with the domain, they will be permanently deleted as soon as you unpark the domain. For this reason, it is strongly recommended that you back up your email messages before proceeding.
NOTES
To park a domain, you must have an already registered domain, and it must be pointing to our servers by either Nameservers or A record.
The parked domain can take a few hours to start working.