Learning software during ARK3 focuses on the necessary tools to document existing buildings as well as developing your own small scale designs.
You should have a good grip on all the graphical tools used in the study, like Photoshop, Illustrator and InDesign, and everyone expects you to handle all the workflows associated with these programs. This semester you will use 3D modeling to aid you in specific tasks, mostly using SketchUp, or if you wish, Rhino.
You should be able to take measurements from real life objects and document them in a precise way in a 3D model, as well as use that information to present drawings and other visualizations. You should also have the necessary understanding to develop a design in 3D in your course work. All of this can be learned in SketchUp and most of the necessary learning is condensed in the Modeling a cabin from measurements-tutorial.
It might be tough trying to choose where to start, so you might have some interest in reading about Choosing a CAD Package.
If you feel like these things are easy and you are already proficient in SketchUp, you could do worse than trying to do the work in Rhino.