Welcome to the forums and to Trainz, rosschris10.
The 1.4GB download is the installer for the T:ANE base package, which will expand to 7.7GB. Once you extract the data, be prepared to wait as it decompresses from the archive. Sit tightly and don't click anything. The progress bar may look frozen, but it's busy working in the background.
Turn off your antivirus while installing to ensure the download can do its thing.
Once that is installed and registered, which I think happens automatically with the online versions, you will then download the extras via T:ANE its self when you start up the actual program by clicking on Start Trainz at the Launcher.
Before you install the program specifically, I would like to make some recommendations.
* When installing, let the program install where it's supposed to be.
* When choosing the location of the content, choose another location besides the C:\Users\{userlogin}\App Data\Local\N3V Games.
You'll be prompted on this location when installing if I remember correctly.
If you have another hard drive installed, use that instead. I for example have mine on my F: drive in F:\TANE_DATA.
There are many reasons to do this, among them is for easier data backup. In Trainz your whole world exists within the data folders and database. By placing the data on another hard drive, or another location outside of the default path, it's easier to get to. The other reason is if your system should need to be refreshed or rebuilt, you won't lose your data. Then as time goes on, you'll discover the world of modding and reskinning, and content repairing, which is made much easier by putting content outside of the App Data path.
* Disable antivirus scanning of your data folders.
And this is about it for now. There's other stuff you can do, but I think this will suffice until everything is installed.
Hope this helps.