With IMAP, each email client synchronises with the emails stored on the server (webmail). This means that if an email is read, moved or deleted on one device, that change is also reflected on the server and any other devices that synchronise will also show that the email has been read, moved or deleted.
For example: If an email is moved to a personalised folder on one device then all devices configured with IMAP will reflect this change an folder will will be visible to all devices/email clients configured with IMAP.
With POP, the copy on the server is automatically deleted once the email has been retrieved by any device unless the email client is configured to leave a copy on the server so that it is available for other devices.
Using the same example as above: If an email is moved to a personalised folder on one device or via webmail, this folder will not automatically appear on each device that accesses these emails unless they are manually added. The email will also need to be moved to that folder on each device, provided that a copy has been left on the server.
The differences between IMAP & POP is also explained on
https://www.telstra.com.au/support/category/email/manage/what-is-the-difference-between--IMAP-and-POP
I hope this clarifies the difference between the two.
- Shelly