When I'm introducing myself to a class or student for the first time, one of the first things I touch on is asking questions. I make it very clear that my classroom is a judgement-free zone, and that no question is "stupid". However, I do provide them with various venues to ask their questions, in the event that they still aren't comfortable asking something publicly. In my experience, just having an option for them makes them feel more comfortable from the start, and they will be more likely to ask questions as they arise.