Gosh, Pete, that's a pretty harsh response to someone who just paid you money and asked an innocent question. I had exactly the same the same question. I purchased the registered version and installed it. Yes, I saw the "Installation and Registration Guide", but no I didn't read the whole thing, nobody does. What I did read were the big red letters on the bottom of the first page which read: "The following pages provide full instructions on Installing and/or Registering FSUIPC4, and Registering WideFS7". So I skimmed through those pages as I ran the installer and entered the registration code. The installation completed successfully, so I figured I was done with the "Installation and Registration Guide", because I had successfully installed and registered the software. Then I spent an hour scratching my head and wondering, "What next?". Nothing installed in the Start menu, nothing on the desktop, nothing in the ZIP file named "User Guide" (and why would I re-read the "Installation and Registration Guide" when I had just finished that step?), no "Getting Started" page on the website, nothing appeared in FSX...
So, for the record, after you run the installer, the User Guide and other documentation for FSUIPC can be found here:
C:\Program Files\Microsoft Games\Microsoft Flight Simulator X\Modules\FSUIPC Documents
or here if you are using a 64-bit version of Windows:
C:\Program Files (x86)\Microsoft Games\Microsoft Flight Simulator X\Modules\FSUIPC Documents
(unless you specified a different folder when you installed FSX)