You need to start by opening "Preferences" & then "Sharing Book by Email" in Calibre.
In the top window, you will need to add an email address as follows:
Yourkindlename@kindle.com and put a check mark in the box next to it.
Make sure you click "Apply" at the top of the window.
Select the book that you want to send to your Kindle and then click on the "Connect/Share" icon on the Calibre menu bar.
One of the choices when the menu drops down is "email to
yourkindlename@kindle.com
that should do it for you.,
cheers