Yes, the 3 angles on on a triangle, always add up to 180 degrees. I've always thought that was cool!
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I found this site about angles on the VLC, grade 6 math guide under Geometry. It has a neat little demonstration tool.
http://www.mathsisfun.com/angles.html
I also found this site on how to use a protractor to measure angles, under Grade 5 Math - Geometry:
(Be sure to watch the video demonstration and try the practice feature!)
http://www.mathsisfun.com/geometry/protractor-using.html
Finally....here is a good YouTube video about measuring angles. The first half of the video is a good for getting the idea of how to measure basic angles like you would find in a triangle, the second half of the video, shows how to do more difficult measurements.
http://www.youtube.com/watch?v=pWfJFkKdVHI
Good luck!