Hi It sounds as if your friend is set up for POP3, which is fine if you only use one device, or don't want your emails to sync with other devices.
If you want to check your email on more than one device, and want them to be up-to-date on each device, you may be best with IMAP. So, emails that you've read on a PC, show that they've been read when viewed on laptop/phone etc, or if you've already deleted emails on your laptop, you don't want them to still be there on your PC when you view your emails there. They sort of synchronize.
This web page, click here explains the difference. If you want alternative explanations, maybe type 'pop vs imap' into a search engine.