If a student asks you a question you need to take a little time to determine whether you should answer or the student should be encouraged to seek a solution.  Is it something the student is expected to know or can easily discover by reading the text or laboratory manual?  Would the student's skills be enhanced if encouraged to try and find an answer and share it with the class?

As a tutor or demonstrator you are expected to be familiar with the content of the course or the procedures covered in the laboratory.  Students will feel you are negating your responsibilities if you seem vague and ill prepared.

This doesn't mean you need to answer every question but there will be times when you feel you should respond but don't know the answer.  It is best to acknowledge this and undertake to find out for the student.  You must then honour your commitment.