Run it through like a regular debit card and follow the screen. It's super easy. If the item counts in it's programming it will go through. Do not be shocked if there is a bit of a balance. The computer will know what to do. It will let you buy approved things until the balance runs out and you can pay the difference.
I do like they went to the card system. The old system you would bring your vouchers and it would just scream "poor" the minute you handed them to the cashier. I felt sorry for people that used these as they needed to use them. Many regulars who saw these went "oh, lord how long is this going to take." with thoughts of treating them like second class citizens for using assistance programs running through their heads.
I am so glad that many of these gov assist programs are going to plastic cards now as it has shifted society away from this mind set. The customers can use their cards with peace of mind without getting these odd stairs like they use to. As a cashier we don't even know you paid with one until the receipt prints. Discrete, simple, confidential, easy.