Both POP (post office protocol) and IMAP (internet message access protocol) allow people to get access to their email from a remote server. However, that is where most similarities end.
POP will download your emails to your computer. But, when you start using more than one computer/mobile device for the same email account you have to delete or file the same email on every device. This will get confusing when you log on to a different device and lose track of which emails have been read, deleted or any of your emails that have been sent to different folders.
IMAP will store your emails on to remote servers allowing the user to synchronise their email using this two-way protocol. This is the more popular choice, with many people using at least 2 devices - their laptop and smartphone.