Once you have completed your course a certificate should become available for the state or province you are certifying for directly from your dashboard, under "Print your Course Certificate". Once you click the option to print the certificate, if you're using Google Chrome typically you should see the download happen at the bottom left of your browser screen.
You should also receive an email within 5 minutes. Make sure to check your junk and spam folder.
See below for a view of what the dashboard with a printable certificate looks like.