I'm not with Laminar Research, just a fellow simmer in the UK.
Basically once you have purchased a valid copy of XP11 from LR directly, you will firstly download the X-Plane 11 installer application and that will download the remaining XP11 flight sim software.
All of the software is completely standalone and does not involve any part of your PC's operating system. You just need one hard drive with enough capacity to accommodate all of the files etc., plus a system spec that meets the necessary requirements.
If you wish to download a valid copy of XP11 onto one PC, then that's fine as you can use your product key to activate it.
However, if as I understand you wish to download XP11 onto one computer and then copy and transfer it to another PC, then that again is fine, as you can now use your product key for that PC instead.
What you can't do however, is try to use two versions of XP11 at the same time whilst online, with just one valid product key. If you attempt to do this, then you may find that LR invalidates your licence!
A word of caution when copying a valid copy of XP11 from one PC to another, please ensure both PC's have the same type of operating system i.e. Window/Windows or MACOX/MACOX.
Also, I wouldn't attempt to download a valid copy of XP11 onto a PC and then try to copy it onto iPad or similar, as it will most likely not function?