Homonyms are words that sound alike but are spelled differently. I just looked up "homophone" since I had not heard this term before. . .and it means the same thing! So, you just taught me something!
As to web sites, have you tried the Grammar Glossary on this site?? Look to the navigation bar on the left of this page. Under "Quick Links" there is a grammar glossary. Also, try looking in the "Students", "Reference" and "Resources" areas via the navigation buttons at the top of this page.
I don't have a site right off-hand, myself, or I'd post the link.
Hope this is helpful! This site is FULL of different help areas!
Sweet Momma Sue