To use HTTPS you will need a certificate. You can self-sign or buy one from a trusted authority. If you are using a self signed certificate for testing you will need to trust that certificate on any clients. The recommended way is to obtain a certificate from an already trusted authority.
There are lots of example on how to generate self signed certificates, such as this one from Microsoft: MakeCert
Place the certificate in the same folder as the Performance Stub executable, then type the name into the stub details including the file extension then add the password for certificate. The protocol for that stub will now change to HTTPS.
To test it browse with your normal web browser, making sure you start with https:// and include the relevant port.
Note: the port doesn't have to be 443 in order to be secure, you can select any free port.