Email message headers have a lot of information in them. Only the tiniest amount of that header information is typically exposed to a recipient by default. There's much more to it than just the from address, to address, subject line and date. There's routing information, authentication information, IP address information, and more information hiding just beneath the surface, in the "full headers" or "internet headers" of that email message. To get at the rest of that header information associated with a given email message, a recipient will need to "view full headers" or "view the message source."
Here's a guide from MXToolbox on how to get full email header information from various email clients.
Google explains how to obtain full headers from Gmail, and even shows you how to extract valuable information from them.
Microsoft explains how to obtain full headers from various versions of the Outlook email client.
Pro tip: When somebody asks you to send them email headers, don't send them a screen shot of the from address or email body. That's not what they're asking for. (And screen shot images aren't searchable; if somebody is trying to help you troubleshoot something, it is painful to have to manually read each line of a header in an image to try to find the right header.) Instead, send them a text file attachment containing all of the copied-and-pasted email header info, or full message source.
December 8, 2017 Update: LifeWire has a great article on how to decode email headers.