The default camera control system in Meshmixer is the Fusion 360 camera system. This is a very simple system where Shift+middle mouse button tumbles (rotates), the middle button pans, and the scroll wheel zooms, as shown below.
This is the easiest system to use for viewing a single model, but it has some drawbacks. Some tools in Meshmixer use the middle button and wheel for frequent operations (such as changing the brush size with the wheel). Also, on a trackpad there is often no middle-button to press, and so this mode will require a hotkey combination.