Spring is an open-source game engine designed to work like the classic RTS game Total Annhilation. You can find lots of documentation and reference at www.springrts.com and a lot of downloadable files at www.springfiles.com. The baseline files you'll need are all linked below.

The way Spring works is by reading in packages that can be downloaded and placed in the Spring folder. This way, people can create mods, maps, and other features for the game, and they can all coexist and be supported without too much mess. This does, however, mean that getting it going requires a few things, so, begin by unzipping Spring onto your USB drive, follow that then download the sample map (DeltaSiegeDry.sd7) and the sample mod (XTA) and place them in the Spring/maps and Spring/mods folders, respectively.

Following that, download the map tools and unzip them into a separate folder (preferably outside the Spring folder -- you'll be working to create a new map from here.