Few questions from a very newbie in jQuery

Few questions from a very newbie in jQuery

Dear people,
I'm a Webdesigner from Buenos Aires, Argentina.
Currently I use HTML5 for customer websites but I want to enter in mobile design.

I downloaded the jQuery version 1.3.0 final and I started some simple designs trying to make a simple page not only for smartphones and tablets, but for desktop navigators too.
After many tests, I started used (additionally) the CSS used for jquery.mobile-1.3.0/demos/index.html page, because it CSS have many classes ready to use.

After several hours of trying, I thought maybe it would not be legal to use the CSS file.
The main reason I started using that file is because, since I am quite new to jQuery, there are many things I do not understand from the CSS provided with version 1.3.0 . I dont know about when and where some things should be applied.
My first question is: cCan I use the CSS that does not belong to the 1.3.0 package in a commercial design?

My second question is:
What should be used for start the designs ot to learn?
- JQuery 1.9.0 from http://jquery.com/download/?
- 1.10.2 from http://jqueryui.com/ jQuery?
- Mobile jQuery 1.3.0?

Thank you in advance for your help and I hope my english can be understood correctly.
Best regards.
GusSiglo21