Hi guest,
I'm not exactly sure how to explain this to you so I'll just show you. Let's take the number 3799 for example, ok. And let's say you get a question that asks you to round 3618 off to two signicant figures. We take 3799 and round off the 99. Now the 3799 becomes 3800. Now just remove the two zeros, because when rounding off significant figures all zeros to the right of the number don't count. So now you are left with 38 which are your two significant figures.
I'm not very good at explaining so if you still don't understand look up this website:
http://www.purplemath.com/modules/rounding2.htm
Happy to help. :)