I would say Edureka have free courses on ethical hacking. You can checkout there.they are very good in clearing the basics of networking but if you want to learn without a particular course you can go for
3) Using windows for hacking
4) Cyber attacks
These things should be on.
Tips otherwise basics will not be clear for ethical hacking.
You can also check out the blogs:
What is Ethical Hacking? - Edureka
You can search out for tons of tutorials on edureka: