In the mathematical jargon

If you have, say, 4 boxes to put the following 6 types of things in:

Apples
Oranges
Pears
Bananas
Gooseberry
Lemon

Such that you could:

a) only put one piece of each of the things in one box; and

b) you could put the same thing in all the boxes, i.e you could put,
say, an apple each in each of the boxes. In the mathematical jargon,
if repetition was allowed

Then, I know that we could have 6*6*6*6, i.e 1296 permutations.

However, I want to know the algorithm to decide what those
combinations are. Help appreciated.