There is a collection of balls in three colours - red, yellow and blue -- and there are as many of each colour as we could want. There are four labelled boxes in order. You want to choose 10 balls and share them between the four boxes. It matters how many of each colour each box gets, but it doesn't matter what order they are in within the box. It does matter what order the boxes are in. It's ok to have no balls in a particular box, and it's ok to have no balls of a particular colour in any box.
For clarification, the following two arrangements are not different:
[RRBY][YYY][RBB] & [RYBR][YYY][BRB]
and the following arrangements are different:
[RRBY][YYY][RBB] & [RRBY][BRB][YYY]