universal tickets??

[momtimesone]

We are going on vacation on July 22 and will be making a one day trip to universal studios On July 26. My question is If I have every intention of buying a express pass for us to use when should I buy my express/ park tickets? I plan on using the electronic pickup so how does the express pass work with the electronic pickup. Do I go up to a customer service desk and show them my reciept for the express passes? Sorry for all the questions this will be our first time at universal and I want to have some knowledge after all Im leading the group.