what is actually meant for BUFFER? how does it work

Buffer is something that is used to hold the data temporarly.
Ex-
If we are watching any thing online,then buffering of data takes place i.e for sometime data get stored in buffer then processed.

Its a temporary location where you can preserve the data. For example when you want to swap 2 nos like x=2 and y=5, so that after swaping you get x=5 and y=2. One method wud be to use a temporary variable like z and copy x value to z, so z=2. Then copy y value to x, so x=5. Finally, copy z value to y, so y=2. Here z is temporary variable and the BUFFER.

Similarly, when you watch videos online, all the data is copied to a temporary location or buffered and then the video can be watched. Buffers are used in almost all programming tasks. Its like a helper to your main task. It does work by itself, it is used by other tasks to make a bigger task possible.