Well if your using 10 (X) and no one has turned off the auto cursor, It should be easy. The problem is that people tend to turn that off because "It didn't work that way in V7. So I dont like it".
If Autocursor is on.... When you move near an object, it will show you the options for attaching the new geometry.
So, If you have an arc on the screen, and you select the Line command, and then move your cursor around the arc slowly, you'll see the icon next to the pointer change to different options.
Mike S. is right Look in the help for AutoCursor.
BTW: Books are one way to go... But Video training make the process a little more obvious. Consider looking at the link below.
Mike Mattera
Tips For Manufacturing Training CD's, DVD's for Mastercam, SolidWorks, Inventor, G-Code Training & More
http://www.tipsforcadcam.com