Lawrence Hall of Science
The Math Page: Skill in Arithmetic: Subtracting Whole Numbers and Decimals
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.
Math Slice
Math Slice: Subtraction: Math Worksheets
This tool allows you to create worksheets where students solve subtraction equations at varying levels of difficulty.