Creating content from multiple .md files?

Sorry I’ve been looking for a little while can’t seem to figure out how to create other content from different content files other than default.md like I’d like to have a product.md and a blog.md is it possible to display them like that or no? If so what’s the line? hugo new posts/my-first-post.md

Do you mean using archetypes?

See Archetypes | Hugo

If you have archetypes/blog.md it will be used when you create new content using

hugo new blog/foo.md

Do you mean that you want the content of one page to be pulled from different .md files ?
if so, Page bundle is your friend

You can also get the content from other sections with GetPage