Parent style.css file is empty. How do I import css to a child theme?

I am new with WordPress and using a theme called Vanquish. I used a plugin to create the child theme since I was having trouble on my own, and it seems to work fine. However, I cannot edit the child theme. I checked and found that the parent theme’s style.css file is empty. Instead it says the following:

/*
* PLEASE DO NOT EDIT THIS FILE!
*
* This file is only in your themefolder for WordPress to recognize basic theme data like name and version
* CSS Rules in this file will not be used by the theme.
* Instead use the style-custom.css file that is located in your themes folder to add your custom styles.
* You can copy a style rule from any of your css files on /css/ folder and paste it in style-custom.css and
* it will override the original style.
*/

So, it seems I can’t import from that file. The problem is, I don’t know where to import from or how. The style-custom.css file just says this:

/* For Novaro's Theme Customization Style */

There’s a ton of php files in the template section of the parent theme. Should I just forget the child theme, and be using the parent theme and the style-custom.css, or would I be better off using the child theme?

If so, how can I edit the child theme so that it actually affects the site’s appearance? I have included the child theme’s style.css and rtl.css contents below just in case that helps.

/*
Theme Name:     Vanquish-child
Description:    Child theme of main Vanquish
Author:         Accio Tokyo
Template:       vanquish

(optional values you can add: Theme URI, Author URI, Version, License, License URI, Tags, Text Domain)
*/

/*
Theme Name:     Vanquish-child
Template:       

Right to Left text support.
*/
@import url("../twentyfifteen/rtl.css");

I notice the rtl.css file is importing from twentyfifteen, but my layout looks fine and is definitely vanquish in the child theme, so I don’t know what that means. As you can see, I’m very green at all this. Anyway, thank you in advance for any help!