If you have any doubts whatsoever about using something on your website because you didn't write it, please take a page from my book of life's lessons and don't use the content!
Get permission to use quotes. Permission can be granted by the author or even a publisher of the content you wish to use. Never quote anything without asking permission! Don't assume that your use is okay. It's not.
Fair Use portion of the Copyright Act
The Fair Use portion of the Copyright Act grants permission to use content under very specific circumstances. You, as a website owner, regardless of your intentions or your claim that you qualify under this provision, are NOT one of the people the Fair Use is intended to protect.
The Fair Use provision covers schools and universities who copy pages from a book to hand out to students. It covers the use of quotes in tests and similar printed material.
If you want to teach something from your website, teach it in your own words. Do the research, yes, use the books to gain the knowledge you lack to fully teach your subject, but don't quote the reference unless you have been given specific permission to do so.
Copyrighting Your Work
Your work, when presented at your website, is protected under copyright law. You have but to place a copyright notice on the work and to retain a copy of it on your computer.
Because you are the originator of your work, your claim to it begins the moment you put the first word on paper or store it in your computer.