Q. How can I send an email to a student in Canvas?

You can use the course E-mailer.

Click "Course E-mailer" in the left navigation, then click the "Members" link in parenthesis. You will see a list of e-mail addresses, one for each individual in the course. Clicking any e-mail address will open up a message in your native e-mail client (Outlook for example). Note that Canvas does not archive messages sent from the Course E-mailer, they are only archived in your sent folder of your native e-mail client.