One of the most important things we can do in our life is to ask questions. It's how we learn, it's how we evolve and grow - personally, professionally, we are all in search of knowledge.
Never hold back, never think of your question as 'stupid', never fear what the person will think if you ask the 'stupid' question because the pursuit of knowledge, for progress and growth is always respected and even if they laugh or look down on you for not knowing, you still get an answer, you're still able to move forward, you've still harnessed that knowledge for your own growth and that's a darn wonderful thing.
If you never ask, you're sabotaging yourself and your progress.
Be fearless. Ask questions.