When you register a domain name, there are subdomains that may be used at no extra domain registration cost. And with that domain name, you could use subdirectories with no extra costs, for organizing the pages of content on the website.
For webmasters and website developers, the question you have to ask yourself and answer is: should I use a subdomain or subdiectory?
Here are 3 factors to consider for informing your decision:
- Subdomains may be configured to point to an entirely different web server, so that subdomain could be used as an entire different website with different functions
- Subdirectories (aka subfolders) follow the same structure as files on your hard drive
- Which would work better for your audience when sharing or publicizing a link: keyword.example.name or example.name/keyword
It’s helpful to learn from the examples of others, other websites’ usage of subdomains. See the list of what’s surfaced as the Most commonly used subdomains, aka third level domains
And there are search engine ranking considerations. That’s a harder issue to answer, because algorithms are constantly changing, so that won’t be attempted here at this time.