Imagine you have 7 buckets in a line, each one representing a day of the week. Monday, Wednesday, and Saturday are full of water reminding you when to call your mother. Unfortunately all the buckets have small holes in them so you have to keep topping them up otherwise you will forget the schedule.
Ok, so this is probably not the best way to remember things, but it is the basis of how memory works in computers — welcome to the world of “dynamic RAM”. Some memory (c.f. static RAM) holds its information as long as the computer is turned on, and some works even when the power is turned off (e.g. that found in a USB memory stick).