The opening screen of Google SketchUp, is in the perspective view. You will see a model named Bryce. Bryce is there to help you with scale and proportion, but most people find him a distraction. You can easily delete him and re-add him or other people at later times in your modeling. You will also notice red, green, and blue lines. This is where the geometry comes in. The red line represents X axis, the green line represents Y axis, and the blue line represents Z axis. The dotted lines represent the negative X, Y, and Z axises respectively.

click to enlarge
Don't worry about brushing up on your high school geometry skills. You won't need much more than a rudimentary understanding of dimensions and space, unless you're planning on doing projects that require precise measurements. SketchUp is extremely intuitive and will help you by predicting your next logical move. You will see as you go along, that SketchUp gives you suggested moves (by way of dotted lines). This is one of the ways this software is so user-friendly.
In order to model with ease, you'll need to get very familiar with your tool bar, and the keyboard shortcuts. Here are the tools you'll need for designing a basic house.