Magnification = focal length of scope / eyepiece.
Your ED80 is F7 so has focal length 7*80 = 560mm therefore your 25mm eyepiece would have an approximate magnification of 560/25 (about 22x).
The true field of view is apparent field of the eyepiece / magnification.
For Plossl's apparent field is approximately 55 degrees so your 25mm eyepiece (assuming Plossl) will have a true FOV approximately 55/22 or about 2.5 degrees (just under at about 2.46).
These are theory numbers - for better accuracy and to take into account that the numbers quoted are not always exact you are better off timing how long it takes a star to transverse the centre of the field (i.e. turn off the motor drive and turn on the stopwatch). 240 seconds equates to 1 degree.
RE: sketching tutorials
Try:
http://perezmedia.net/beltofvenus/archives/000567.html
and:
http://www.cloudynights.com/ubbthrea...oard/Sketching
As possible starting points.