By purchasing an application, all three platforms?

Hello. It is very enjoyable for me to cooperate with you.
Please answer my question. I want to do my shopping after answering my question.
Question: We want all three platforms, Android and iOS and Windows.
On the Purchase page, just one section to enter the number. If we enter 1, then we can get one of the three platforms? Or one license for all three platforms, but can we use one system? Or what does it mean if we enter the value of 3?
Please explain this.

Thanks for your inquiry.

One license will be valid per application on a single operating system.
So to support all three platforms, you need 3 licenses.
At purchase time you need to specify only the number of licenses (3 in your case) needed and the type (standard, professional or premium).
Latter during license activation you will specify the platform and package name/bundle id...