How to have specific category posts navigation?

So much to read, so it obviously requires plenty of work to do before it functions. Isn’t there already a plugin for it? I’m sure it exists somewhere, I’m just not sure what or where to look for. I would like to have previous/next post inside my actual post, not in the side bar or wherever else.

It does work perfectly well, almost exactly what I wanted. Would it be possible to have this function inside the post (at the bottom of it)? Because at the moment it’s outside of the wrapper area.

I don’t really think that it would depend on theme, but thanks anyway, I’ll try and search for other similar plugins!