How do the number of digits I have influence how many different combinations of digits I can have?

The number of digits available dictates how many different combinations there are. For example if I could use up to three decimal (base 10) digits, the maximum number of combinations I could have would be 10³ = 1,000. That is, I could represent all of the numbers from 000 to 999. If I had 4 binary digits (bits), The maximum number of combinations I could have would be 2⁴ = 16.