There are many things about poems. Some people teach an entire college course about poems. Here are a few basic ideas.
Poets are given the right to write in any way they like. It is called "poetic license" as if they have the right to do anything they want with words, like my short poem "Phar out." That's the entire poem. It has no title!
However, poetry comes in many forms like Japanese haiku or traditional Chinese poetry or "eight-legged essays" that might be considered poems.
Many poems have "meter and rhyme." Meter is the sound or pace of the poem, often with the same number of words per line and emphasis. Example:
This poem, you see, is very short.
I hope it doesn't make you snort.
That short poem rhymes (short/snort). It also has meter, a pattern of an EMPHASIZED and an emphasized syllable and eight syllables per line so it can be read as:
THIS poem, YOU see, IS veRY short.
I hope IT doesN'T make YOU snort.
When you read it, you can feel the pattern. That's only one pattern. There are many.
I like this poem, if you can call it that. I wrote it in 1994.
Spaced! The funnel front ear! Thesis the voy agers of the easter shipping prize. Ets five emission: "To sneak out gnu life, two explode new worlds, too goldly go wear know won has gone beef or."
Does that make no sense to you? I'm not surprised. I took a famous saying from a 1960s TV program and used poetic license to mutilate it into something only Trekkies would recognize. The original start of the TV program Star Trek started with these words:
Space! The final frontier! These are the voyages of the starship Enterprise. Its five year mission, "To seek out new life, to explore new worlds, to boldly go where no one has gone before."
Despite my changes, when Americans who are my age read that, most of them recognize it!
That's a college course in poetry in 500 words or less!