Iambic pentameter is a pattern of stressed and unstressed syllables in a meter of poetry. An iamb is a foot of unstressed/stressed syllables. Pentameter means there are a 5 feet of unstressed/stressed syllables in a meter (line of poetry). This establishes the rythym of the poem and iambic pentameter is most closely related to the rythym of normal speech.

It sounds like this: 

baBOOM / baBOOM / baBOOM / baBOOM /baBOOM

A sonnet is of 14 lines, usually in iambic pentameter, "with rhymes arranged according to a fixed scheme." Here are the two main forms of the sonnet:

Italian: Major group of 8 lines (the octave) followed by a minor group of 6 lines (the sestet)
English: 3 quatrains followed by a couplet.

All of Shakespeare's sonnets are written in predominately iambic pentamenter. So sonnet 130 is written in iambic pentameter, as is Elizabeth Barrett Browning's sonnet 43.

Now review both sonnets and try to follow the rythym and determine how iambic pentameter is used in both poems.