I am having a hard time to understand how to use the PHP type. Could you clarify a little how do I create a variable that has a valu dynamically evaluated from PHP code? (If this is what it is supposed to do)

Yes, this is what it is supposed to do.

You simply need to return a string from the PHP code you enter in the "Script" text box.

Example:

This code would result in the current year as a value of the content variable.