Ever noticed how traveling to somewhere new seems very far? But on your 2nd trip it's short, well that's how browser cache works. On the first load of the page it takes longer just like the first trip, then the browser stores some data in the systems memory, just like the way your brain stores images of landmarks or buildings in your memory. So on your return trip it recollects the images, making the journey seem shorter, same thing with the browser, it retrieves the store data from the systems memory saving it the trip to the servers thus making the page load faster.
Just some random illustration that came to my mind could be used to explain to someone.