what will i fill out in IMAP path prefix

Hello iPhone6plusAnne,

If you're looking to use iCloud Mail on a device that doesn't meet iCloud system requirements, this page that you may have come across will help to provide info on the needed server settings: iCloud Mail server settings for other email client apps - Apple Support

In the screenshot it looks like you're filling out the information for the incoming iCloud Mail server, which the page provides the following for:

IMAP information for the incoming iCloud Mail server

•Server name: imap.mail.me.com

•SSL Required: Yes

If you see an error message when using SSL, try using TLS instead.

•Port: 993

•Username: This is usually the name of your iCloud Mail email address (for example, johnappleseed, not johnappleseed@icloud.com). If your email client app can't connect to iCloud Mail using just the name of your email address, try using the full address.

•Password: Generate an app-specific password.

Note that the 'IMAP path prefix' in the screenshot is optional, so you may try leaving that blank.

Cheers.