I’m not sure if you still need help. The portfolio.php acts like WordPress’s page.php, you can customised the page you like. As for single-portfolio.php, it acts like single.php, you can customise the single post.
If you’re not sure what to do with it, I suggest you copy whatever that’s in page.php, do the same thing to portfolio.php. Same for single.php & single-portfolio.php. Hope it helps.