Significant figures are about determining and dealing with the error associated with measurements. Below is a ruler and an object being measured. What is the length of the gray object assuming the other end of it starts at zero. Make your measurement as exact as possible.
In your guess for its length, the 10's place is known with certainty. In other words it is definitely 20 units long. Your number in the 1's place is a guess. the one's place is an estimated measurement. Next look at the measurement with a more precise ruler.
by Tony Wayne ...(If you are a teacher, please feel free to use these resources in your teaching.)