Some email software requires you to choose between POP/POP3 and IMAP protocol settings. As a rule of thumb, you should always choose IMAP if you’re planning to set up your email address on multiple devices (e.g. home computer, iPad and a smartphone). This ensures that all of your devices will get a copy of every email you receive.
A computer or device using POP protocol for an email account will often download emails from the mail server and then not leave a copy for other emails to download. For example, this means that once an email is downloaded to your desktop computer, you can’t download another copy on your smartphone.
Some email clients may have an additional setting to make POP accounts leave a copy of emails on the mail server, but this is not always the case.
If you only use a single computer, choosing POP should be fine.