To add a new subdomain in Plesk Control Panel, you can follow these steps:

Step 1: Log in to your Plesk Control Panel using your username and password.

Step 2: Once logged in, you'll see the Plesk Dashboard. Click on the "Websites & Domains" tab.

Step 3: In the "Websites & Domains" section, locate the domain under which you want to add a subdomain and click on its name.

Step 4: On the domain's overview page, scroll down and click on the "Add Subdomain" button.

Step 5: In the "Subdomain name" field, enter the desired subdomain name. For example, if you want to create a subdomain called "blog" for the domain "example.com," you would enter "blog" in the subdomain name field.

Step 6: By default, Plesk will create a subdirectory with the same name as the subdomain within the domain's root directory. If you want to specify a different directory for the subdomain, you can enter the desired path in the "Document root" field.

Step 7: You can leave the "PHP support" option as the default unless you have specific requirements for the subdomain.

Step 8: If you want to secure the subdomain with an SSL/TLS certificate, you can select the appropriate certificate from the "SSL/TLS certificate" drop-down menu. If you don't have an SSL certificate, you can choose to obtain a free Let's Encrypt certificate by selecting the corresponding option.

Step 9: Once you have entered the subdomain details and made any necessary selections, click on the "OK" button to create the subdomain.

Step 10: Plesk will now create the subdomain and update the necessary configurations. You'll see a confirmation message once the subdomain creation is successful.

That's it! You have successfully added a new subdomain in Plesk Control Panel. You can now upload your website files or configure the subdomain as needed.