Accessing CSS file

Hello

According to this page

https://en.support.wordpress.com/custom-design/editing-css

To access the CSS editor, go to Appearance → Customize → CSS in your blog dashboard.

Yet, when I click on Appearance | Customise, I only see Site Title & Tagline, Colors, Header Image, Background Image, Navigation, Static Front Page. I don’t see any CSS file.

Basically, I need to change a font in the Header and, in the main window, I would to like to justify text.

WordPress seems to use the word ‘blog’ a lot. For example, in the ‘main blog’ as if it’s synonymous with ‘window’ as in ‘the main window’. Is
that right? I usually think of a blog as an online diary not as a normal Web page.

Can I also ask: is it possible in WordPress to upload and use my own images?

Thanks!