How to send an email with Arduino and a WiFi shield? I want to make my Arduino connect via WiFi and then send an email. The idea is very simple, but the problem is that I've never worked with those protocols and other things before. I just wanted something that's already premade, so I would just change the information.

Is there a library or a function that sends the email?

If someone could help me to understand, so I can make it myself, that would be the best.
What you're looking for is a SMTP (Simple Mail Transport Protocol) library. A Google search finds 2 for the Arduino:

SMTPClient
This seems to be a minimal-capability SMTP-only library that piggybacks on top of a connection library.

FullIP
This seems to be a full IP package for the Arduino that works with select network devices which includes SMTP capability.