page is what comes out of Hugo at the end. A
post is the default
content type in Hugo. (There are no pages and posts as you know it from WordPress, if you know WordPress, but even there they are nothing else than two custom post types).
If you don’t add a date in the front matter then (in my experience) the post is dated January 1st 1970.
What you want to achieve is probably something like this:
You add what you call
posts into the posts directory, which makes them of content type
post and you can loop over them. the about-us and contact-us folders are your “pages”.
If you would add multiple files into contact-us you have a content type contact-us and you can loop over it too. You probably can loop over it with one single markdown file too, but why would you
So to answer your question: it’s all the same. If you create a folder below
content you create a content type named by the folder name. create a folder called projects, put some markdown files with projects in there and you have a post type projects.
I think post(s) is used in Hugo only as a default content type, so the templates in layouts can refer to something.