Theory:

Alliteration is the occurrence of the same sound at the starting of two or more words in a single line, in a poem.
  1. The slender smiling girl.
  2. The song of sweet birds.
  3. Black bug bit a bear.
  4. Practise the piano.
  5. Feel the phone on your face.
  6. Dandelion whose fuzzy head.
What are the uses of alliteration?
 
1. It creates a rhythm, similar to rhyming words.
2. It emphasizes the importance of phrases.
3. Mostly used in tongue-twisters.
Alliteration used in the poem "The Shed":
  1. When I’m in bed I lie and I listen,
  2. When I’m in bed I lie and I listen,
  3. There’s a dusty old window around at the side
  4. There’s someone staring at me
  5. I’ll peep through that window one day.
  6. My brother says there’s a ghost in the shed
  7. Who hides under the rotten floorboards,
  8. I know that there isn’t really a ghost.
  9. My brother tells lies to.
  10. And the spider has been gone from his web.
Important!
The lines "I’ll open that door one day", "I often think there’s", "Each time that I pass", "I’ll peep through that window", "He’ll jump out and chop off my head", and "I’ll go into that shed one day soon" DO NOT contain alliteration though they have words that start with the same letter.
 
The reason is that they have different sounds. For example, the letter 'O' in the word "open" sounds like 'O', while the same letter in the word "one" sounds like 'Wo'.