Here is a site that has helpful information, especially in Science, Math, and Computer Science. https://www.khanacademy.org/ It is also good for ALL grades including elementary and junior high.
Here are two sites that have helpful information, especially in English. www.schmoop.com and www.sparknotes.com
Need help understanding Shakespeare? Here's a GREAT site. It translates the text into modern language.
Haing trouble understanding novels to need to read for English? Try this site: