IMAP (Internet Message Access Protocol):

IMAP allows you to access your Gmail emails on multiple devices while keeping them synchronized. When you read, delete, or move an email on one device, the changes are reflected on all devices connected to the same account.
POP3 (Post Office Protocol):

POP3, on the other hand, downloads your emails to a specific device and usually removes them from the server. This means actions on one device (like marking an email as read) won’t affect other devices.
App Passwords:

App passwords are used when setting up non-Google apps or devices that require access to your Gmail account. They are generated through the Gmail security settings and act as a substitute for your regular password. This enhances security, especially for applications that don’t support two-step verification.