An SSL certificate is a digital certificate used for encryption and authentication of websites. By installing an SSL certificate, you can ensure that communications between the website and visitors are securely encrypted, preventing data from being tampered with or stolen, and increasing visitors' trust in the website. The site group server can install an SSL certificate to implement HTTPS encrypted access to the website.

　　The steps to install an SSL certificate are usually as follows:

　　1. Purchase an SSL certificate: Choose a trusted SSL certificate provider and purchase a certificate that suits your website needs. You will get the certificate file and private key file.

　　2. Prepare the certificate file and private key file: Upload the obtained certificate file and private key file to your site group server, usually through FTP or control panel.

　　3. Configure the server: Configure the relevant settings of the SSL certificate on the server, such as specifying the paths to the certificate file and private key file, configuring the SSL encryption protocol, etc. The specific configuration method depends on the server software and operating system you use.

　　4. Testing and verification: After completing the configuration, test and verify by accessing the HTTPS address of the website. Make sure the HTTPS link is working properly and displays the correct SSL certificate information.

　　Please note that each site needs to be individually installed and configured with an SSL certificate to ensure that each site can be accessed securely via HTTPS.

　　In summary, the site group server can install an SSL certificate. By using an SSL certificate to implement HTTPS encrypted access, the security and credibility of the website can be improved.