450px by 450px with a transparent background.  

No less than 200px by no less than 200px with a transparent background.

The logo in the top left of the browser, can be a jpeg or png file and should be 32px by 32px.

This is in hexadecimal format and will be the main colour of your platform. The text will be predominantly white so it is best to stick to dark colours.  

This will appear next to the favicon on at the top of the tab.

The Meta description will appear underneath the Meta Title in a search engine.
Find out more here https://searchenginewatch.com/2016/05/26/how-to-write-meta-descriptions-for-seo-with-good-and-bad-examples/  

Remember to press save to make sure everything is published to your platform. Use the “Go to Platform” link in the header to view your changes.