How to customize/design a custom post?

I am learning WordPress and I’m a bit confuse about custom post type. What I knew about it is that it works like the category and tag, if I’m not mistaken.

I am creating a simple e-commerce site and there are pages that automatically created. I guess it’s because of some content I added (adding products and product category). I know those pages are not “Page” at all ‘coz it’s not in the Page tab. And I think it’s a custom post, if again, I’m not mistaken.

My question is, how can I design that page? I mean design using css, add widgets, or other things just like a normal page type?

Thanks!