I am new to 3D, and would like to join 2 cylinders at right angles to one another, and clean up the corners where they intersect, so that the appear mitered.  Any suggestions? Thanks for the great forum.

Copy your original objects twice.In the first pair of cylinders subtract cylinder A from cylinder B.In the second pair of cylinders subtract cylinder B from cylinder A.Combine the results.  If you like what you got erase the original cylinders.  If you don't start over and use a different technique.
John Connor2013-04-05 18:24:45

The original cylinders are on the left.  The mitered ones are on the right.
John Connor2013-04-05 18:27:30

John, Thanks for the help.  I am trying create an "L" shape where the cylinders are cleaned up at the corner, rather than the "T" that you described. Thanks!

Use the SLICE command then.  Or sweep a circle along a path that represents a 90 degree corner.  Either or both should work.

John Connor2013-04-09 18:28:47