Khan Academy
Khan Academy: Equivalent Fractions 1 (Denominators 10 & 100)
Practice writing equivalent fractions with denominators of 10 and 100. These problems give you pictures to help you find the answer. Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video...
Other
Chili Math: Adding and Subtracting Fractions With Same or Like Denominator
Features steps on how to add and subtract fractions with the same denominator.
Wikimedia
Wikipedia: Fraction
This one page website provides a basic explanation of a fraction and its denominator and numerator.