The chief component of a poem is words, although they don't have to be real words. Lewis Carroll's famous poem "Jabberwocky" is a combination of real words and words invented by the poet. Poets choose their words very carefully and try to get precisely the right word in every case. Poetry is a medium where meaning can be very rich, so word choice is key. Lord Byron alludes to this need for precision in his work "Childe Harold's Pilgrimage."
Poems are organized into lines, and quite often, each new line contains a new thought. Lines can begin partway through sentences and don't need to begin with capital letters. America's most popular contemporary poet, according to the New York Times, is Billy Collins. His poem "Fishing on the Susquehanna in July" is basically seven complete sentences organized over 13 sets of three lines. The length of the lines helps convey a poem's rhythm.
Victorian poetry, written by former poet laureate Alfred Lord Tennyson, Robert and Elizabeth Barrett Browning, and others, tended to feature rhyme. As reported by literary critic Thomas Edmund Connolly, Algernon Charles Swinburne said, "...a rhymeless lyric is a maimed thing." Free verse, which is without rhyme, became the dominant mode for poetry in the 20th century. Poetry of the 21st century tends not to have rhyme either but the fashion may change before the century is out.
Regardless of whether it has rhyme or is written in free verse, a poem tends to have some organization. This may be evident in the poem's ideas, structure or intent. A stanza is an organized unit within a poem, which may also be a verse. Poems also have rhythm, conveyed by single words, phrases and lines. Usually too, poems have underlying ideas and themes. Metaphors, symbols and alliteration may be used by a poet to help convey these thoughts.