There’s rarely a bright and unambiguous line between free verse poetry and prose, but I’d argue poetry is about layered use of language to a degree you generally can’t sustain for the length of most prose genres. Line breaks are one way to draw attention to the way a word or image is used, which is one reason you see them often in poetry, but it’s not distinct to poetry, nor is it something all poetry uses extensively.

Like many distinctions, this one breaks down at extremes. Microfiction can seem a lot like a poem and narrative epics can look a lot like prose, for example.

Read a lot of poets, and find one you like. Try to imitate their style, the way they use language. It won’t be good at first, but that’s normal, and it’ll help you find your own way of writing quickly. From there, it just takes practice.