The e-mail is a fast and important means of communication. Person A can contact Person B across the ocean using the Internet.
Alice at firstname.lastname@example.org sends an e-mail to Bob at email@example.com. To get there, the e-mail first goes through a the Submission Protocol (smpt.a.org) which sends it to the Domain Name System for domain name verification, which sends it back to the Submission Protocol, which gives it to the Message Transfer Agent (mx.b.org) which gives it to Bob. That is the process of the e-mail.