The "branching fraction" is the fraction of decays that occur in a particular channel; all of the branching fractions for all of the decay channels must add up to $100\%=1$. This is a graph predicting how a Standard Model Higgs would decay as a function of its mass, which was much more interesting before we managed to measure the mass of the Higgs at $\rm125\,GeV$.
So this graph tells you that a very light, $\rm80\,GeV$ Higgs would decay about 80% of the time into $b\bar b$, about 9% of the time into $\tau\tau$, and so on. There's a mass region around $\rm170\,GeV$ where the Higgs would decay into something like 98% $WW$ and 2% $ZZ$. Reality, around $M_H = \rm125\,GeV$, seems to be where the $ZZ$ and $c\bar c$ channels are equally likely at about 2.5%.