Viewport Navigation

 1) Movement physically

1) A = Left

W = Up

S = Down

D  = Right

2) Head movement

Holding down the scroll wheel on the mouse allows you to not move physically but rotates your view much like a head around the level to see what is around you.

3) Saving camera viewports

to save a view or position you want to return to hold ctrl + F1. This allows the view to be saved so if you lose where you are you can return to this view later. To return to the view hold shift + F1.