Alliteration is the repetition of the same sound at the beginning of a group of words.
Poets use alliteration to help create mood, rhythm or emphasis. It can also help with memorization. It's important to realize that it's all about sound, not spelling. For example, the letter c can have a hard or soft sound as in cereal and cat. These two words next to each other would not be considered alliteration because they are not the same sound. Examples of alliteration are:
The speaker and the neighbor repair the wall from opposite sides. The speaker and the neighbor repair the wall from the same side. The speaker repairs his side of the wall while the neighbor watches.