In the base 6 number system, we would only use numerals from 0 to 5. The idea of base 6 is just like the normal base 10 system, however instead of using the numerals from 0 to 9, we use numerals from 0 to 5. And instead of having a ones digit, a tens digit, a hundreds digit and so on, we use a ones digit, a sixes digit, a thirty-sixes digit, and so on. Therefore in base 6, the number 321 means 1 one plus 2 sixes plus 3 thirty-sixes, or 121. So to count until 15 for example, we would need:
Base 6 Base 10
1 1
2 2
3 3
4 4
5 5
10 (1 six plus 0 ones) 6
11 (1 six plus 1 one) 7
12 (1 six plus 2 ones) 8
13 9
14 10
15 11
20 (2 sixes plus 0 ones) 12
21 (2 sixes plus 1 one) 13
22 14
23 15