Instead of starting with a tool like Tableau, try the book "Data Smart" by Chief Data Scientist at MailChimp, John Foreman.
It talks you though all sorts of data analytics problems step by step - and you only need Excel (or the excellent free Libre Office Calc) to do most of the examples.
My problem is that I also need to keep earning at the same time I am learning :( That is why I wanted to start with Tableau, as it seems it is possible to pick up some contract work with Tableau?
