A Shakespeare play basically is a long poem written in blank iambic pentameter, or unrhymed lines of five “feet” of two syllables each, with accents on the second syllable of each foot (as: da-DUM, da-DUM, da-DUM, da-DUM, da-DUM). For example, when Prospero brags to Ferdinand about his daughter Miranda:

Do not smile at me that I boast her off,

For thou shalt find she will outstrip all praise (IV.1.9-10)

Readers can find the stresses in the lines like this:

Do NOT smile AT me THAT i BOAST her OFF,

for THOU shalt FIND she WILL outSTRIP all PRAISE.

The thing about iambic pentameter is that it sounds close to regular English speech. So even though it is carefully crafted, actors can recite their lines and still speak in a natural-sounding rhythm, even if their diction and syntax are very different from what modern audiences are used to.

A style of poetry and story-telling arose in France and Italy during the Middle Ages called blank verse, which is unrhymed iambic pentameter. English authors, especially Chaucer, adapted it into the form used by Shakespeare.