Adding a cusomizable pop-up window with instructions to fields

Adding a cusomizable pop-up window with instructions to fields

Hello,
it would be very helpful, if it was possible to be able to add a pop-up window to each field with instructions what and how to fill it.
I think we all struggle with the fact that employees fill in data incorrectly - format, content, etc (although having a very detailed manual what and how to fill the fields). This requires extra work correcting the data afterwards.
This could be limited if there was a customizable pop-up window with a short instruction what and how to fill in the field. 
Miroslava