It allows the server to sync your mailbox between all the devices and keep everything up to date. IMAP is a special communication protocol between a client and a mail server. This one is severely outdated, and nobody should keep using it. As to POP, just ignore this ancient protocol. You need to make sure the IMAP Status is set to Enabled.
After that, go to the Forwarding and POP/IMAP tab. Log into your Gmail account and click on a small gear in the right top corner of the window.
