1) Take a piece of paper and a pencil and write the numbers from 0 to 20, like this:
0 -
1 -
... and so on, then write their names, like this:
0 - Sıfır
1 - Bir
... and so on
2) Now on another paper write the number names below and then the numbers which correspond to each:
On altı, İki, On sekiz, Dört, Beş, Yedi, Altı, Sekiz, Dokuz,
On bir, Üç, On iki, On, On üç, On dört, Sıfır, On beş, On yedi, Yirmi, Bir, On dokuz