Mac OS/X supports "modifier keys" that can be used in conjunction with a mouse.
For example pressing the Ctrl key on the keyboard and clicking the mouse (left button if using a multi button mouse) invokes a context menu and Shift + click allows multiple selections.
When gestures is used to generate presses then these modifiers will perform the same actions as when used in conjunction with a mouse or trackpad.
However, there is a few built in modifiers in Gestures:
Control + pinch/spread will zoom the screen
Control + two finger drag will pan the screen when its zoomed
Holding shift while zooming or panning the screen will cause it to zoom or pan more slowly, allowing for refined adjustments.