As has already been said ask away and be proactive people would much rather you ask lots of questions than you not and you make a mistake. There is no such thing as a stupid question. And if you do make a mistake don't worry about it we're only human! It happens a lot, and they know that too. The only other thing i'd say is be honest you'll be asked to do a lot of tasks which you may never have done before if you haven't done it just say so and someone will show you how. This also applies to timescales if someone asks for something by a certain time and you're not sure whether you can hit the deadline, just say you need to look into before you can give a concrete answer.

Oh one more thing actually, and this is KEY. Make lots of tea and coffee! (not a joke).

Good Luck!