Google Analytics shows porn pages; can't find them in WP

When looking at Google analytics, I get a list of pages like [my site]/ipad-porn, [my site]/ebony-porn, [my site]/celebrity-porn-pics. If I do a Google search of the non-profit that I work for with these keywords, the page doesn’t show up. However, when I type in the specific url, it takes me to a page with inappropriate text but it has my website’s background/template.

I’m an extreme novice to all of this, so how do I get rid of these “pages?” I understand the concept of referral spam (I think), and that I can filter it with Google Analytics, but I don’t know how to fix the problem so that people cannot type in that specific url and see the inappropriate text on what appears to be my site.

I’m so sorry to sound so dumb and ignorant, but I’m completely out of my element here. If anybody can help, I would really appreciate it. I searched for similar posts, but I couldn’t find an answer that I could understand.