Hello Rk B,
In general, you need to be a licensed customer to open support tickets. There are some exceptions though - if you are currently utilizing a valid trial license of the product, then you can also open a ticket. Otherwise, the best support option is to come here to the community and post your question.
Contact your Tableau Account manager via the Contact Us link below (if you don't have one) and they can help get you going on a licensed trial.
I hope that helps out.
What Patrick said! The other exception is: You can be a 'licensed customer' that hasn't maintained your yearly support agreement so you are NOT entitled to support.