Simply print off the confirmation email, or show the confirmation email on your smart phone when you arrive at the garage. They'll then locate your tyres and get about fitting them to your vehicle for you.
Your confirmation order will contain details of who to contact at the garage if there are any issues, a map, and your order reference number which will begin EW.
It's sometimes neccasary to check if your tyres require a locking nut (see vehicle handbook). If so there will usually be one in your vehicle with the puncture repair kit, or often in your cars glove box. Inform the garage upon your arrival of this and if neccessary provide it to them so they can remove your wheels.