I know it is a scary thought, to begin a conversation in a new language.  But total immersion is the only way, you need to jump in the water in order to learn to swim. 

From my experience of teaching, I know that to get people talking from the first moment is really important. It is better to say something wrong and to be corrected than not to say it - it's ok to make mistakes. 

Many people spend years studying grammar but cannot hold a simple conversation because they lack vocabulary and conversational skills. So the question is not "when" the question is "how".

You start communicating when you feel you are ready to benefit from the experience.