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 in the number. 

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