basics about aircraft & helicopter

The FAA publishes several training manuals for Airframe and Powerplant Mechanics. I don't know of a web site for basics, but these manuals are not that expensive $20-30.

I am not sure at what level your interests lie, but I was an aircraft mechanic and QA inspector for 12 years and feel that it is important to start with the basics of aerodynamics.. For specifics as they relate to helicopters this page is quite thorough http://www.helicopterpage.com/. I hope that this helps.

Try this site: http://en.wikipedia.org/wiki/Aerodynamics. The rotor of a helicopter works pretty much as a combination wing and propellor, hence the name rotary-winged aircraft for them.