1. Log in to your Plesk panel.
2. Navigate to your domain dashboard, where you will find an option labelled "Security," within which there is an option called SSL/TLS certificates.
3. Click on the SSL/TLS Certificates option at the bottom of the page. Then click "Install a free basic certificate provided by Let's Encrypt" and proceed with the installation.
4. You can select the second option to enable SSL for the domain with "www." included, as well as for webmail. Click "Get it free" to proceed.
5. After clicking "Get it free," you will receive a TXT record for the verification process. Add this record to your domain DNS and then click "Continue".
6. Once the DNS verification is completed, you will see a screen like this.
7. You can also check how many days remain until the SSL certificate expires by visiting "https://www.sslshopper.com/ssl-checker.html".