Help with Microeconomics?

I'm stuck on tried to understand About the Equimarginal Rule in this particular chapter which talks about combining two activites where the marginal benefit per dollar for the first activity equals the marginal benefit per dollar for the second activity. Even after reading the textbook im not able to cope up and understand how it works because they havent used simple examples. Can someone please explain it to me with a few examples if possible? Any help is greatly appreciated.