Sorry I didn't have much time to get to this post yesterday.
With regard to what magnetic field lines are made of - these are mathematical constructs, handy ways of looking at electromagnetism that really should be done away with but are too useful.
At a small scale forces are generally seen as carried by an exchange of virtual particles, the bosons.
Virtual particles flash in and out of existance in particle and anti-particle pairs - the more massive a virtual particle the shorter its life.
Electromagnetism is carried by photons, these are massless so the range is effectively inifinite.
The weak force is carried by W and Z bosons which have mass so this can only act over a short range.
From the nature of the questions you ask you seem to be in that difficult stage where you're fairly famillar with the topics at the popular science level that most TV programs go to but not ready (or interested) at a formal mathematical academic level.
If that is the case I could strongly recommend this book
http://www.amazon.co.uk/Facts-Mysteries-Elementary-Particle-Physics/dp/981238149X
One of the best I've read in explaining some of the more modern concepts in the field - but still very accessible even if it is 10 years old now