When you count to 10, the numbers are
1, 2, 3, 4, 5, 6, 7, 8, 9 and 10.

The numbers from 10 to 100 are:
10, 11, 12, 13, 14, 15, 16, 17, 18, 19,
20, 21, 22, 23, 24, 25, 26, 27, 28, 29,
30, 31, 32, 33, 34, 35, 36, 37, 38, 39,
40, 41, 42, 43, 44, 45, 46, 47, 48, 49,
50, 51, 52, 53, 54, 55, 56, 57, 58, 59,
60, 61, 62, 63, 64, 65, 66, 67, 68, 69,
70, 71, 72, 73, 74, 75, 76, 77, 78, 79,
80, 81, 82, 83, 84, 85, 86, 87, 88, 89,
90, 91, 92, 93, 94, 95, 96, 97, 98, 99,
100.

You can see a pattern in these numbers.  Each number has two digits.   Each time you count up, the second digit increases by 1 unless the second digit is a 9  (24, 25, 26, 27, 28, 29).  If the second digit is a nine (such as 29), the first digit increases by 1 and the second digit becomes 0.  The next number after 29 is 30.

The first digit is called the tens place.  It tells you how many sets of ten are in the number.  The number 24 has 2 sets of 10.

The second digit is called the ones place.  It tells how many ones there are in the number that are not included in the full sets of ten.  In the number 24 there are two sets of ten plus 4 ones.

The number 24 could be represented by:
 

The 2 in 24 comes from the two full rows of 10.
The 4 in 24 comes from the third row which has 4 in it.