In Fusion 360 how do I select an entire 3D object, not just its sides or faces? I'd like to mirror a triangular prism I made. However, whenever I select it I am only able to select the faces or sides.

Is there a way to select the whole 3D object to move or mirror it?
Selecting the body in the browser will select the entire body. Clicking on the body in the viewer will only get you faces or edges.  

A long click (click and hold) on the model will give you options on what to select. You can choose a face or body under "Depth" or choose a body or feature under "Parents."