Choose any poem to read out loud.
Read the poem in a natural voice and do not try to look for anything special. You will start to notice that certain words are more stressed than others. This means there is usually more inflection on certain words which comes out naturally.
Mark the words with stress with a small "/" symbol. You can also mark the unstressed words with an "x" symbol.
Decide which meter you are reading with these clues. If the poem works in a pattern of unstressed, stressed, unstressed, stressed, repeat, it is "iambic." If the poem is stressed, unstressed, repeat, the poem is trochaic. If the words all all stressed in a row, the meter is spondaic. If it is unstressed, unstressed, stressed, the meter is anapestic. If it is stressed, unstressed, unstressed it is considered dactylic.
Decide which words in the poem are stressed. If the meter is iambic, the stressed syllables are called "iambs." Count these iambs and that will determine the word to use to describe it. For example, if there are five iambs, the meter is considered "iambic pentameter." If the meter is trochaic, the stressed syllables are considered "trochees." The meter of a line of poetry with four trochees is "trochaic tetrameter." In an anapestic line, the stressed syllables are "anapests." Three anapests would be called "anapestic trimeter." In a dactylic line, the stressed syllable is a "dactyl." A line with six dactyls would be "dactylic hexameter."
Evaluate if your poem has a consistent meter. Many poems do not have a meter and are considered "free verse."