In each of these examples, the alliteration occurs in the words that have the same sound. As you can see:
• Not every word must be alliterative. You can use prepositions, such as of and pronouns such as his and still maintain the alliterative effect.
• Alliteration does not need to be an entire sentence. Any two-word phrase can be alliterative.
Even some single words can be alliterative, if they have multiple syllables which begin with the same consonant sound.