I assume what you mean is: how do you interpret a plot on log-log paper? Given the equation y = Ax^k, take the log of both sides and rearrange to get:
log(y) = k log(x) + log(A)
Let Y= log(y) and X = log(x), and the plot on log-log paper will be:
Y = kX + log(A)
This is an equation of a straight line, with slope = k and Y-intercept for X=0 (i.e. x = 1) of log(A). Hence you can read the value of A directly off the graph for x=1.