How to understand residual, and how to relate it to trash. Please explain the residual based this paragraph: Residuals are what remain after removing...

How to understand residual, and how to relate it to trash. Please explain the residual based this paragraph:

Residuals are what remain after removing all the information from the data. Since they should carry no information, we consider them as "trash." It is necessary to make sure that we do not throw out any trash that has value (information) and that can be exploited to better explain the behavior of the dependent variable.

Please give me help, i need to get answer before 1pm today 02/17.

thank you so much