You have some rectangular icon image files that are advertisements. You want to post them for your advertiser in your WordPress website. What should you do?
Possible Solution #1 (if you can provide CSS code)
1. Log into WordPress
2. Appearance -> Themes
3. Find which theme is active and click "Customize".
4. Click "Additional CSS"
5. Insert the CSS code you want
6. Optional: if you need to upload an image, click "Site Identity", click "Upload files", then upload the file you want.
Possible Solution #2
Log into WordPress. Go to Settings -> Ad Inserter. There will be different tabs for different blocks.