the best place to go to be honest with you is type the technique you want to learn in youtube and you should at least get 3-4 different versions of defenses, submissions, etc...
i say it the best place because it it the most user friendly, cheap, and fast. there are plenty of others if this doesn't suit you, but they usually cost money. also i think ATT is doing some online stuff now too. not exactly sure what the website is maybe attonline.com, but i think that is free as of now too