I used to use this website called 'gcserevision101.files.wordpress' it is really good for notes. I only used it for unit 1 and 2 though because they now make you pay for the notes, i think its five pounds for access to all the notes. If you want to pay that money then that website is hugely helpful.
Hope this helps :)
Other than that all I can suggest is this website or bitesize :P