First of all, you should have a purchased SSL certificate for your website on hands. If you don't have a certificate, you can use a free certificate issued by Let's Encrypt (see instructions above).
Note: It is possible to use Plesk for generating CSR (Certificate Signing Request) for your certificate. For that, navigate to Domains > example.com > SSL Certificates, fill in the required fields and click Request. Such certificate will be Self-Signed and not valid for checks.
Log in to Plesk.
Go to Domains > example.com > SSL/TLS Certificates > Advanced Settings.
On the SSL/TLS Certificates page, add your certificate:
Note: If you are experiencing issues with a certificate installation, contact your certificate seller and ask for certificate installation instructions for Plesk.
If an SSL certificate is stored in a single
Click Browse... to select a certificate file. Then click Upload Certificate.
If an SSL certificate is stored in the form of
Click Add SSL/TLS Certificate and scroll down to the Upload the certificate files section and upload these files. If both the certificate and the private key parts of your certificate are contained in a
*.pem file (you can check it by opening the
*.pem file in any text editor), just upload it twice, both as the private key and the certificate. Click Upload Certificate once finished.
If an SSL certificate is stored as a text:
Click Add SSL/TLS Certificate and scroll down to the Upload the certificate as text section. There, paste the certificate and the private key parts into the corresponding fields. Click Upload Certificate when you have finished.
Once the certificate is created, go to Domains > example.com > Hosting Settings and:
Open your website at https://example.com.
Note: In case of any issues, make sure that the certificate was properly selected.