Need Requirement Analysis Software Visio 2012 or Altova

I have recently started working with some business analysts which doing jobs like requirement analysis, UML diagram, & flow charts I am amazed to see that they are using tools like Visio 2012, Altova etc.
But I am very unfamiliar with these tools and now I want to learn how to use them or how to start some over these applications like software Visio 2012, Altova or any other tools for my requirement?
