First thing you need to do is purchase one of the McAfee suites, which contain ePO. With the purchase comes a Grant Number via email.
Next login here:
Use the Grant Number (Download My Products) and press Go
Something like this should be returned
ePolicy Orchestrator : xnnxx-nxxxx-xxxnx-xxxnx-xxxxx
Your number will be different.
This is the number you need to use within ePO to take it from evaluation to production mode.
You do not need a license key to evaluate ePO; license keys are only provided for purchased products. You have 90 days to evaluate ePO before the evaluation period expires, and it is fully functional during that time. As Ron mentioned to you, if you purchase the product, you receive a license key and the product becomes licensed (with no expiration).
In addition to ePO you will need point products to manage (e.g., VirusScan Enterprise). Once you have ePO installed, and are running in Evaluation mode, you can use the Software Manager feature to install evaluation versions of a number of point products. It's possible that some of the point products have limited functionality during the evaluation period and that should be conveyed in the documentation.