Hi yokpimnara
Thank you very much for your question.
It depends when are you leaing your country to come to Switzerland.
If it is in more than a month, you can purchase it with the order form, and wait for the SwssPass (with the half fare travelacard o it) card directly at home.
If you are coming to Switzerland soon, there probably is not enough time, and the best option is to purchase everything directly at the Zürich Airport Station. You will be able to use it directly.
I wish you a pleasant day.
EleonoraS