I was going to suggest the Owl at Purdue as well! Here's a link:
http://owl.english.purdue.edu/They have a section for 7th-12th grade students that might be a good place to start.
I also enjoyed a book called "Eat, Shoots, and Leaves" by Lynne Truss. It is a quick and funny read. Your local library might have a copy. My library also has a used book section where you can pick up books for a nominal donation (a buck or two). There are always a lot of writing texts in there.
I think that you know a lot more than you think you do. Your writing on this forum is intelligent and easy to follow. I didn't know a lot of the English terms for the parts of speech until I started to learn them in Spanish. If you were to ask me to explain what a future progressive verb was in English, I wouldn't have been able to explain it until I learned it in Spanish (By the end of my senior year,
I will have been taking Spanish for three years). I think that your issue is more with terminology than knowledge and application. I respect your desire to better yourself though. I am here because I share the desire to better myself!
Have you ever done Adlibs? They really helped me as a kid to understand some of the parts of speech. It asks you to fill in nouns, verbs, adjectives, and adverbs and then you read back the story with nonsensical (and often humorous) results. My parents did Adlibs with my brother and me when we were young . . . until they got tired of us saying poop for every noun, pooping for the verbs, poopy for the adjectives, and poopily for the adverbs. I guess we were just that age for the bathroom humor.
Here are a couple of websites that give you an overview of the English parts of speech and grammar:
http://depts.gallaudet.edu/englishworks/grammar/partsofspeec h.htmlgrammar.about.com/od/terms/a/topgramterms.htm
Eric Noto