Hello,
When you are writing content in the individual post or page then you see the categories at the right side from which you can add or select categories and assign to the pages and posts you want.
https://prnt.sc/quvlsw
About adding icons to the School activities section you can follow the path Admin panel > Appearance > Customize > Section > Features
About the little blurbs in school activities, you can follow the path Admin panel > Appearance > Customize > Section > Features and add content in the ‘Section Description’.
You can also refer to the screen record for further clarification.
https://www.loom.com/share/5ada0c22c5614114b702c6c43d38c36d?focus_title=1&muted=1
Hope this helps.
If you have further queries, let us know.
Thank you.