A lot of people appear to be unaware of the existence and purpose of this domain and often unintentionally advertise someone else's domain when asking questions on forums.
The example.com domain is completely different from all other domains on the web in that it doesn't belong to anyone and is available for everyone to use. Its purpose is to serve as a generic substitute for any domain name at all when explaining how to do something or asking a question about something where you don't want to specify a particular domain name.
The idea is that the person reading an explanation that includes the use of example.com references can simply substitute whatever their own specific domain name is for example.com throughout.
Using example.com in explanations or questions is not advertising a specific domain as if you actually go to that web site it simply displays the message "This domain is established to be used for illustrative examples in documents. You may use this domain in examples without prior coordination or asking for permission." The 'more information' link that follows that message takes you to a web page that explains what IANA managed reserved domains are - a page that tells us that example.org is reserved for the same purpose as example.com and therefore should perhaps be used where we need to identify a second generic domain that is not the same as the first.
So basically example.com (and example.org) both do and don't exist as they are not regular domain names that can belong to anyone but are specifically reserved for use when referring to a domain name in documentation where the actual domain name can vary.
For people asking questions in forums you should either specify the real domain name you are asking about or specify example.com if you don't want to identify your domain. On no account should you use any other domain name since even though some of the names may appear generic they still actually belong to someone and using them in your question both advertises their site and also might imply that you actually own that domain.