You have three shirts and four pairs of pants.  How many outfits consisting of one shirt and one pair of pants can you make?
One way to approach this is to use the multiplication principle: if there are n choices for one thing and m choices for another thing, then there are n times m choices for both things together. In this case, there are three choices for a shirt and four choices for a pair of pants, so the number of outfits is 3 times 4, which is 12. 