How many 6 number combinations can be made from six numbers?

You dont say whether zero is included or whether a digit may appear twice. These are the various answers:
No zero, no digit more than once in same number: This is any 6 from 9 in any order which is factorial 9 divided by 6 ie 60480
No zero, digit may be repeated: 9 to the sixth power: 531441
Zero allowed in any position, no digit more than once in same number: This is any 6 from 10 in any order, which is factorial 10 divided by 24 ie 151200
Zero allowed in any position, any digit may be repeated: 10 to the sixth power, ie 1000000.
Finlly, if you regard 123456 as the same combination as 123654, then answer is any 6 from 9 which is a mere 84

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There is only 1 combination of 6 digits out of 6. Order does not matter in combinations so 123456 is the same as 342516 ect. One of the consequences is that there are no "leading" digits and so the presence, or otherwise, of 0s is irrelevant.

If, instead of 6 out of 6, the question were about 5 or fewer out of 6 then whether or not the 6 were all distinct will matter.