They can rhyme, but they don't have to. They can be serious, or they can be funny. They can be short, or they can be long. Here is a very interesting collection of poems from people around the world. You can even send your own poem to them, and if it's good enough, they'll put it on the web site.
Poetry is a very different kind of English.
It's about using English to create a mood or a feeling in people. Poetry doesn't have to always follow the rules. It can rhyme or not rhyme. It can use words, phrases, or sentences. You can use any style you want, and you can choose any subject.