3D Mode is the default viewing mode where you are free to see the model from any direction
Zoom in / out - you can either use your mouse wheel or if you have a touch pad on a laptop , use two fingers to pinch together (zoom out ) or push apart (zoom in).
You will notice a small yellow dot in the model, which is the locus of rotation or “Target” ie if you hold the left hand mouse button down and drag the mouse the whole model will rotate about that point. See below, the Target is indicated with a red arrow:
To change the Target, hold down the right mouse button and move the model to another location. Because mouse movements on a screen are only two-dimensional, in order to move the Target in all three dimensions, you may first need to rotate around it.