When you first learn some information, the first place it goes in your brain is to your short-term memory. So, you read something, or hear something, and it stays in your short-term memory for a little while. If you don't hear it again, or that information doesn't get repeated, it is likely to disappear from your memory - you will forget it. However, the more you repeat that information, the more likely it is that it will be remembered, that is, it will enter your long-term memory and stay there for a long time.
Hope this helps :)
