Can I learn English online? What is the best website?

Sure you can, I suggest www.alison.com

http://alison.com/learn/English

This seems to be a nice site.

I used Englishtown.com.

According to the feedback on the website and what I hear from people, the website is the best ESL program taught online.

Try it out; here are the costs of using it:

http://www.englishtown.com/ar-sa/study-plans-and-prices/