Iambic poetry is measured in groups of syllables called "feet."
One foot = "da DUM"
Iambic pentameter has five "feet,"or groups of syllables, usually (but not always) sounding like this:
"da DUM, da DUM, da DUM, da DUM, da DUM"
Shakespeare used it quite often - here is an example from Macbeth, when Lady Macbeth says to Macbeth after Duncan's murder:
"And wash this filthy witness from your hand."
(and WASH this FILthy WITness FROM your HAND)
Or in Twelfth Night, when Duke Orsino says:
"If music be the food of love, play on."
(If MU sic BE the FOOD of LOVE play ON)