Rounding to significant figures has many uses for example if a journey is 6924 miles long then it would be much easier to round it up to the nearest thousand, 7000 miles.
To round to a significant figure you
If rounding to the first significant figure you look at the first digit that is NOT 0.
Look at the digit after the one you are rounding to. eg if rounding 6924 to 1 SF, look at the 9.
If the digit is 5 or more then you round up. eg 583 to 1 SF would round to 600.
If the digit is 4 or less then you round down. eg 543 would round to 500.
fill in any spaces to the right of the rounded number with 0's.