Mail tutorial please

Where can I get a tutorial than explain in simple terms how I can access two email accounts using iCloud and also be able to delete some emails on one product without it deleting on another Apple product? My email filing is in a total mess. I have an iCloud account and I can get both my Gmail and iinet account on my iMac, but my iPad is cluttered up with so much stuff I just want to get rid of most (not all) of the emails there that are already duplicated on my iMac. I believe I can just get a required selection I want from iCloud as and when I want, but don't know how. Should I just save the wanted emails into a separate file on my computer and delete them all in mail ?