I am not from Laminar Research; just a flight simmer from down under.
The official and original version of X-Plane is developed by Laminar Research (LR) and can be purchased from this link at https://www.x-plane.com/ This Q & A site only deals with problems being experienced by x-plane flight simmers.
In purchasing from the developer you can get good support either through this forum or you can get support direct from Laminar. One of the LR staff members has been assigned to answer queries from X-Plane users when they have problems. Your direct purchase from LR then supports the ongoing development work.
When you start X-Plane you will often receive a prompt that an upgrade/update is available for download. The download and installation is immediate before you commence your next flight.
X-Plane can also be purchased as a disc version directly from LR or from a licensed/ authorised reseller. The disc version has a problem whereby Disc 1 has to be installed in the DVD drive at all times. The trend nowadays is to delete DVD drives from PCs so a digital download version is the way to go but you need to be connected to the internet at all times.
Unfortunately there is another version of X-Plane available on the market known as Steam. It is a 3rd party hybrid version of X-Plane taking a commercial advantage of the development work by LR. I don't support the product for these reasons. Laminar Research has no connection with the creators of the Steam version. Any X-Plane updates created by Laminar are slow to be made available by Steam.
The installation of the LR version of X-Plane is quite simple, provided you follow the instructions whereby the software is installed in a single directory on the desktop as C:\desktop\username\x-plane or can be installed onto a dedicated drive in the computer. This simplicity allows for the transfer from say the desktop to a dedicated drive within the same computer or if you upgrade your PC..
The important issue is to make sure your keep a backup of the digital download and file away a copy of the digital password provided at the time of purchase. It is amazing the number of flight simmers who lose either one or both and then ask for help in this forum.
Other versions of X-plane create a more complicated installation pathway.
X-plane does have the ability to be installed on any number of computers as required but can only be legally used on one computer at any one time. To operate more than one copy at any one time you will require additional product keys.
Good luck with your purchase and welcome to the world of X-Plane.