The SD Card (200 MB) file is a binary image of the contents of the SD Card you need to boot Galileo, if you are using the IoT dev kit.
BY starting a Linux workstation with the Debuian Live USB image, and booting Galileo from the SD Card image you have a development environment where you can develop using Eclipse on a PC (running the Debian Image) and have the code automatically installed onto Galileo. You can even use the PC to debug code live on Galileo. In other words you type all your code into eclipse on the PC, then you can step through the code one line at a time while it is actually running on Galileo.
It's a bit like the Arduino ide, except you are writing native Linux code, not arduino code.