W3.org teachs you about html,I think its some kind of online class or tutorial but I think you should try to attempt to learn yourself. If you have the time to do it thats what I would do .

Yes, it is a series of tutorials teaching HTML that is hopefully W3 compliant. However to get beyond basic web pages a little more tends to be needed. It's a good start though!

A lot of websites I have built don't pass W3 standards but render just fine in all browsers. I think passing W3 checks is stressed a little too much unless you have a major website then it is a good idea to make sure it certifies.

its not just W3 , its W3C.org , its called World Wide Web Consortium,

The question is how is the learning curve? I mean is it worth my time to even take time out to learn from it?

Truly that depends on what your end goals are. What are you going to be using it for and will that pay off, financially?

I think its not that necesarry that you code your site according to W3C standars , unless you are using that site for your own purpose , if yo are going to sell it and your client asks for it then you have to do that , else its not required