Can someone explain what a subpage is in wordpress? Does it look any different from a regular page? What is its purpose and what does it do?
The only difference between a page and a subpage is that a subpage contains it's parent in the URL, as will any pages that sit as children to the child page...
and so on...
Aside from the URL there's no other differences i can think of.
Subpage is a page, but hierarchical depend from parent. When using automatically built menu will be arranged in this hierarchy.