Numbers, such as 84, have two digits.  Each digit is a different place value.

The left digit is the tens' place.  It tells you that there are 8 tens.

The last or right digit is the ones' place which is 4 in this example.  Therefore, there are 8 sets of 10, plus 4 ones in the number 84.

   8 4
   | |__ones' place
   |_________tens' place

The tens' place value of 2 in the number 24 is due to the presence of two full sets of 10.
The ones' place value of 4 in the number 24 is due to 4 units that are not included in a full set of 10.