Logarithms are only able to make an equation linear if it is an exponential function. For example, [tex]y= e^{x} [/tex] can be made linear by taking the natural logarithm of each side, causing it to become [tex]ln(y)=ln( e^{x})[/tex]. After some simplifying, you are left with [tex]ln(y)=x[/tex]. You are then able to plot ln(y) vs. x to get a linear fit.