You must have Mapsource 6.0 or later on your PC to load and open the StateTopo.exe file. This map executable file is the same file that is on the physical CD. Once downloaded, you double click on the StateTopo.exe file and it will automatically unpack and install into Garmin Mapsource. You are purchasing the downloaded StateTopo.exe file, no CD-ROM or any physical product will be shipped to you.
This is not the full contents of the CD/DVD, rather the self install EXE file for Mapsource. It does not contain the Gmapsupp.img file, see FAQs. You build the Gmapsupp.img file using Mapsource.
Save the download email, it is your only Proof of Purchase, if you wish to upgrade at a later date or purchase the full retail version within 30 days of the download.