Because it doesn't try to do everything for everyone SketchUp is very easy to use. Arguably the most intuitive program on the market. Two key features make SketchUp unique. Polygons are created by drawing the outline of a shape. The inside is automatically filled.
Snap tools help the designer align new lines to existing ones and make it easy to draw right angles.
Since it's hard to describe a visual interface with words you should take the time to watch a small online demonstration . A more thorough demonstration is included with the trial download. In addition to being useful for architects, SketchUp is useful for video game level designers. Sketching allows game developers to quickly layout a level and see what it looks like in 3D. This basic model can then be exported to the usual animation and modeling tools as a .dxf file. To really be helpful for game developers SketchUp needs to do a better job of outputing triangles.