So when they are comparing two functions, let's say one is exponential and the other is linear... and lets assume that the linear one crosses the exponential making itself a secant line...
so if i ask you to tell me when the exponential is going faster, can i use natural logs to figure out where it's going faster?
if yes, how can i use it.
You don't need to, as long as you have it graphed, you can tell at which point the line and the exponential function intersect (if intersected at 2 points pick the one in which the functions are pointing or travelling at), and then determine which function is going to that point faster.
An exponential function is basically a log function, so technically yes. (Graph w/ a logarithmic function).