Difference between Trash and Deleted Messages? Sent and Sent Items?

No difference. eM Client may use different terminology for folders than what appears on your server, or in other email clients, so Deleted Messages is called Trash, Sent Items is called Sent, and Spam is called Junk E-mail. 

Many thanks for your reply, Gary. Just so I understand: the list of folders for my main eM Client email account is: Inbox, Sent, Trash, Drafts, Junk E-mail, Deleted Messages, Notes, Older Receipts and Sent Messages. For my second email account the folders list is: Inbox, Sent, Trash, Drafts, Junk E-mail, Archives, Deleted Messages, Junk and Sent Messages. Are you saying some of these folders are merely redundant? And why would there be an Archives and a Notes folder in one account but not the other? Same for Notes and Older Receipts. Why is both Junk and Junk E-mail together in the second folders list? Is there any difference between Junk and Junk E-mail? The Local Folders section is the simplest: Inbox, Outbox, Sent and Trash. I hope I’m not being pedantic but I would like to know why there are so many folders! Thank you again.    

This really depends on what folders are on your server.

Local Folders are not synced with a server, so the standard folders only.

In your main account Deleted Messages, Notes, Older Receipts and Sent Messages are not standard folders. They may have been created by your provider, by you, or by a mobile app that is connecting to that account.

The same for your other account with folders like Archives.

Belated thanks for this detailed explanation.