I'm just back from a holiday in the Engadine, and took full advantage of the offer.
To travel on local trains and buses, you simply need the PDF they sent you. You don't have to show it to the bus driver - they trust you. (In decades of taking holidays in the region, I've never seen a ticket inspection on a bus.)
You can use it on the day of arrival, but the area of validity doesn't extend very far along the main railway lines.
To travel on the mountain railways and cable cars, you have to get a card a bit like an Oyster card to tap on and/or off. It's free, but there's a 10 franc deposit. There are two ways to get it:
1. Use the link in the email to pay in advance online. If you do this, you will be sent another PDF with a QR code that you can use at automated ticket machines 24 hours a day to collect the card. We did this, and it worked beautifully (of course - this is Switzerland).
2. Take the PDF to any cash desk at any cable car or mountain railway station and they'll give you the card in return for 10 francs.
The card will be pre-programmed for the days you're entitled to. When you're finished with it, take it to any cash desk (it doesn't have to be the one you got it from) and hand it in. You'll get 10 francs back.
The mountain railways and cable cars can charge up to 100 francs for a return journey, and you can easily save more than the cost of the hotel.
If you mislay the email or don't receive it, contact your hotel and they can arrange for a new one to be sent.
You're supposed to carry ID matching the name on the pass, but we have never been asked for ours.
