A decimal is a point or dot we use to separate the whole number part from the fractional part of a decimal number. The decimal point separates the whole number from the fractional part.
Example: In the number 258.16, the decimal point separates the whole number 258 from the fractional part 16, which is 16 hundredths.
And for significant figures if there is a zero between two non-zero digits then it is a significant figure.
For example; 4.5006 have five significant figures.
Zeroes at the end or on the right side of the number are also significant.
For example; 0.500 has three significant figures.