All this drawing is great, but how do you bring in work you're doing in other programs (graphic design, sketches, GIS maps, CAD drawings, etc)?

Importing Images
Bringing image files into SketchUp is pretty easy. Just go to File > Insert and then pick the image you'd like to place. Click to set the origin point and then move the mouse to decide on the size (use the dimensions box in the lower right). Then build your model on top of it. Here's an example of an imported base map with a basic massing model drawn on top of it:

The image doesn't have to be just for a base map. You can put images in anywhere. On a building. You could make it into a component. Etc., etc.

SketchUp and GIS
Since this is a basic tutorial, we will not go into a great deal of detail about using SketchUp and GIS, but it should be said that this is one of the most fantastic attributes of SketchUp especially for the landscape architect. Here is a quote from the SketchUp help files:

"The SketchUp ESRI ArcGIS extension package allows you to create 3D images, within the context of an ArcGIS geographical model or multipatch, within SketchUp without loosing important ArcGIS geographical information. To achieve this operation the extensions export a “geo-context,” or contextual information about the ArcGIS model, which can then be imported into SketchUp. You can then use SketchUp to create 3D models, such as buildings, within the imported geo-context. Finally, you can export the new SketchUp model and import it back into ArcGIS which will automatically position the 3D multipatch exactly as it was positioned in SketchUp relative to the same geo-context. In this way, the user need not worry about world coordinates while working within SketchUp."

Once you learn GIS, this will make a lot more sense! But, for now, know that you can use the two programs together to create wonderful work!