Websites to learn data analysis and visualization?

I'd say you have four choices, all of which are great learning resources so long as you put in the effort.

1. Youtube Videos: This should be more of a supplement to the other resources. If you unsure of a concept introduced in one of the other three resources, then looking it up on Youtube often gives a bunch of useful videos explaining it in more depth.

2. Websites like Khan Academy: These sites have many videos on all sorts of topics, and statistics is definitely one of the more popular due to its enormous amount of applications in a wide variety of industries.

3. Free Online University courses: Harvard, and many other top universities such as MIT, have launched a large amount of free courses on their EdX platform. These are, from my experience, easier to learn from than sites like Khan Academy due to the fact they're based on professional courses and taught by experts in their respective fields. They have the option of paying for a certificate, however most of the courses are completely free to complete. They have a lot of statistical courses such as Big data, machine learning, etc.

4. Textbooks: Textbooks can be expensive, but it's very easy to find free textbooks online, as well as free university notes on university websites. For example, when I studied for my acturial CT1 exam, instead of spending over a hundred dollars on study material I was able to use Warwick University's lecture notes which covered the syllabus absolutely free. If you're interested in probability instead of more applied statistics, I'd personally recommend "An Introduction to Stochastic Modelling" by Karlin and Taylor, there are many free copies online.