The vector bosons W+ and W- are electrically charged, and like the Z0, have mass: 80 GeV. W+ is the antiparticle to W-.
In the initial very hot universe, both light and heavy quarks could be created. As time passed the heavy quarks decayed into the lighter particles we see around us today. These particle transformations were mediated by (among others) W particles, therefore these where very common in the early universe. Using experiments, e.g. at the LEP accelerator at CERN, we can recreate and observe the effects of the heavy W particles.
In the chapter "Picture analysis" you will learn more about how to interpret pictures where W0 particles have decayed. In the chapter "Particle collisions" you can find suggestions of exercises that can be solved by analysing pictures of WW-decays.