A subdomain is an additional part to your main domain name. Subdomains are usually created to organise and navigate to different sections of your website. A normal domain would be example.co.uk where as a sub domain would be xxx.example.co.uk with the xxx’s being replaced with something such as Store.
What are the benefits of using a sub domain and do you need them for your website?
You may have a section of your website that is large enough for you to create a mini standalone site such as an online store. You might want to be able to make bigger changes to this without affecting the rest of the site. If you build a shop on a sub domain you will find it easies to make the changes you need whilst keeping the other sections of the site as they are. The sub domain site will need to contain search engine friendly content and assets such as meta date which should be unique to that specific page. Once live and indexed you can actually gain better results by having a site that is completely tailored to a specific subject rather than trying to get one page ranked well on your main site.