On Pantheon, Select Create a New Site similar to the frame shown below.
You will then be directed to the following webpage shown below.
You will then taken to another page where you will select what platform you wish to use. Select Open Enterprise Pro.
From here, you will be given the link to you site. You will want to click on it which then prompts the installation of Open Enterprise Pro, fill all required information. This will now allow you access to your own Open Enterprise Pro website with demo content that can be edited.