There are different ways to structure a poem and sometimes these will arise quite instinctively. For instance, the metre known as the iambic pentameter (an iamb is a metrical foot of two syllables with the first unstressed and the second stressed), is the nearest to the stress patterns that we use in the English language and will come naturally as we compose. Our lines will be regulated by the metre. A rhyme pattern might also arise instinctively as it creates rhythms that structure our words and lines.
Free verse which does not follow a regular metric or rhyme pattern is another way to arrange our ideas and words. It is not, however, prose that is simply divided into lines. It developed because poets were endeavouring to find freedom from what was thought of as the restrictions of the metric line and rhyming patterns. They wanted to lose the strictly grammatical and syntactical and to have a choice over line lengths and lineation. This style enables a reader to define where the poet, by the automatic reflex action of breath control, persuades a reader to pause. Both vowel and consonant patterns are given careful consideration when writing in this way. When reading poetry written with such freedom it can be seen that alliterative touches are often introduced to create a flowing effect within lines. This does depend on the subject matter, for if the whole tone of a poem is intended to be strident then a flowing effect would not be required. A more lyrical effect can be introduced by placing clusters of vowels and/or consonants in lines as well as alliteration.
All of these techniques can be used to achieve an effect in free verse that is not introduced by rhymes and chimes.