Wordpress editor layout is now changed, so the menu looks a bit different than it used to. To edit the webiste appearance, logo, colors, fotns, menu or widgets in this layout, you have to click on Design
and then choose Customize
Then you should see this customization menu:
You can also see the Appearance
link in Wordpress Admin menu, when you click on WP Admin
in main menu:
You can edit theme source code or CSS, when you have an appropriate rights and permissions. If you have an account with free plan on wordpress.com, you can't do modifications in theme's HTML, CSS or PHP code. This is a reason why appearance editor could missing in your account.