The Intelligent Investor: The Definitive Book on Value Investing. A Book of Practical Counsel by Benjamin Graham

Its not an online course, but it's a great book! It has a lot of information in it, can be dry, but I'm really enjoying going through it so far. Warren Buffet has quoted it in his shareholder letters and other talks.

Link: https://www.amazon.com/Intelligent-Investor-Definitive-Inves...

Also check out Warren Buffets shareholder letters, they are packed with great insights into investing.