Hello,

These three articles will get you going:

http://processing.org/learning/overview/
http://processing.org/learning/drawing/
http://processing.org/learning/color/

You can check the Reference page for the functions, at http://processing.org/reference/.

I guess you can generate the circles automatically or through mouse click, and use variables/arrays to store their center points - then, use those points to create the starting and ending point of the lines.

Good luck!

Take a look at Traer Physics
http://www.cs.princeton.edu/~traer/randomarboretum/