I would suggest starting in SketchUp, drawing lines and boxes and get familiar with the navigation for about 1 - 2 hours and then start using PlusSpec. You will learn a lot about SketchUp by using PlusSpec anyway but it always good to learn navigation first.
You must have a 3-button mouse; the Mac mouse with the slide simply does not work in Sketchup
To Orbit you push your scroll button in until it clicks, and then move your mouse, and you will Orbit around the model
Zoom is simply by scrolling in or out ( You can change the direction is Sketchup settings
Pan push the scroll wheel until it clicks and push “Shift” on your keyboard Or, if your fingers will let you click the left button on your mouse and click the scroll wheel at the same time.