The number "2000" has one significant figure.
-Any number that is not zero is significant.
23463 = 5 sig figs.
-Any zero that is between two significant figure is significant.
3405 = 4 sig figs
-Leading zeros are not significant.
000345 = 3 sig figs.
-Trailing zeroes in a number that contains a decimal point are significant.
24.3000 = 6 sig figs.
The idea of significant figures is to easily quantify the level of accuracy you are treating your figures with.