There are a few different ways to orient a view.  The first, perhaps most obvious, is using of datum planes and FRONT, RIGHT, TOP, etc... Just like orienting a view for sketcher.

Another way is dynamic orientation using VIEW > SPIN/PAN/ZOOM (in v.20) or VIEW > ORIENTATION > ANGLES (in previous versions).  With dynamic orientation, you can rotate the part with respect to the screen (or spin center in v.20) about the Horizontal (H), Vertical (V), and Normal (C) axes of the screen.  In other words, the view is oriented with respect to the screen (or spin center), not to geometry on the part.

With dynamic orientation the order of the movement is important.  If you rotate NORMAL 30 degrees then VERTICAL 30 degrees, the result will be quite different than rotating VERTICAL 30 degrees then NORMAL 30 degrees.  In version 20 the icons in the ORIENTATION dialog box make this much clearer.  Play with it a little to see the results. 

To set a view orientation as DEFAULT, you can use the ENVIRONMENT settings, OR set the default in your config.pro.  Pro/E has 3 selectable settings for the default view:  ISOMETRIC, TRIMETRIC, and USER_DEFINED.  Isometric and trimetric are pre-defined orientations shown below:  (The equations are from Olaf.)

   Vertical   = -45
   Horizontal =  35.26439
     = ArcSin(1/(Sqrt(3)))

- Due to rounding errors in Pro/E, use the value: 35.26379

The proportion of the sides with respect to the view is 1 : 1 : 1.

   Horizontal =  51.57
   Vertical   = -22.91

The proportion of the three sides with respect to the screen view is approx. 1 : 3/4 : 8/9.

ORIENTATION ISOMETRIC

ORIENTATION TRIMETRIC

   Vertical   = -20.7048
 = ArcSin(Tan(ArcSin(1/3)))
   Horizontal =  19.4712
     = ArcSin(1/3)

The proportion of the three sides is 1 : 1 : 0.5.

   Vertical   = -40
   Horizontal =  30

A generic default view - something close to Isometric that's a little easier to visualize.

(This is my personal favorite.)

   Vertical   = -15
   Horizontal =  10

A simple, easy to visualize default view orientation.

ORIENTATION  USER_DEFAULT
Y_ANGLE -40      (This defines the VERTICAL indicated above.)
X_ANGLE  30      (This defines the HORIZONTAL indicated above.)

NOTE:  The order of  X_ANGLE  and  Y_ANGLE  in the config.pro is important.  Notice that the TRIMETRIC view above requires the  X_ANGLE  (Horizontal) first.

ALSO NOTE:  If the  X_ANGLE  and  Y_ANGLE  lines appear without the  ORIENTATION  line, Pro/E will assume it is the default view you desire.

If you wish to have access to more than one of these views in a part, build a mapkey to orient the part as desired and save the view using SAVED VIEWS.  This can be a real time saver especially if you wish to use one of the views on a drawing.

I hope you enjoyed this information.  Once again I'd like to thank Olaf Corten for some of the above information.