If you are looking for a website that explains and defines subtraction with decimals you have arrived at an excellent resource. There are even practice problems at the very end of the lesson.

This site is an online lesson plan and practice problems for students learning how to add and subtract two decimal values are provided here. Detailed explanation of both the methods and the practice questions are provided for easy...

Sixth graders use estimates and work on strategies for adding and subtracting decimals.