An iambic foot (iamb) has a short syllable followed by a long syllable (SL or U/).
Hexameter is six feet per line.
Those drops, like tears from heaven, fall this dreary day;
I see the puddles forming, dimpled with the rain.
And with no sun or sky of blue, my heart does play
with sadness while my mood reflects my inner pain.
Sandra M. Haight – from The Pain of Rain
A closer look at the feet in this poem
U = short syllable; / = long syllable; | = division between feet