MicroMasters™, Professional Certificate, and XSeries program certificates are automatically issued when you have received a verified certificate in each of the individual courses in the series.
When your certificate is ready, a link appears on the Program Details Page. To access the Program Details page, go to your edX dashboard, click the Programs tab at the top, then click the particular program. A link to view the certificate appears in the upper right.
See also What does a program certificate look like?
For information about receiving individual course certificates, check out "How are edX certificates delivered?"