Suppose I have 6 shirts, 4 ties, 3 pairs of pants, and 2 pairs of shoes. If an outfit requires a shirt and pants and shoes, and can either have a tie or not have a tie, how many outfits can I make?

There are 6 choices for the shirt,

there are 3 choices for the pants,

there are 2 choices for the shoes,

and there are 5 choices for the tie (4 ties plus no tie)

for a total of 6 x 3 x 2 x 5 choices for the outfit.