There are several reasons why you may want to assign more than one domain name to a website:
1. Changing the Domain Name
When changing the domain name for a website, it's best practice to catch any traffic still going to the old domain name and forward it or redirect it to the new domain name. This is important especially if the old domain name is getting good placement in search results.
2. Client Owns Multiple Domins
Some businesses have unique names that may be difficult to spell or that are known by multiple variations, or that are known by both the singular and plural versions. It's sometimes beneficial to purchase domain names that cover all these variations so that if consumers decide to type in one of those variations, they should still see the website.
There are other reasons too, but no matter what the reason, let's talk about how this can be done. Since only ONE domain name can be officially pointed to a website (let's call this the primary domain name), the other domain names would need to be forwarded to the primary domain name by the domain registrar or web host. So if the primary domain is siteswan.com, you should setup domain forwarding from wherever you manage the other domain names from, to point to: https://www.siteswan.com. Because every domain name registrar and hosting provider has a different interface, we do not have step-by-step instructions for all of them, but you can take this info to your provider if you need help with setting up the forwarding.