Hi there!
In this excerpt from Richard Lovelace's "To Lucasta Going to the Wars", the lines that use iambic trimeter are:
"To war and arms, I fly",
"The first foe in the field",
"A sword, a horse, a shield".
An iamb is a metrical foot with an unstressed syllable followed a stressed syllable.
On the other hand, an iambic trimester is a meter of poetry with three iambs per line, resulting in a total of six syllables. This meter was common in Greek tragedy and comedy, and it also was the meter in which verses were spoken.
Hope it helps!