Hey there!
Alliteration is the repeating of sounds in words in a single sentence or phrase. An example would be something like "Alice’s aunt ate apples and acorns around August." This is an example of alliteration since the "A" sound repeats 8 times. Remember that not every word needs to start with the same letter or sound for the sentence to contain alliteration; it can usually be considered alliteration if the sounds repeats at least three times or so in the same part of the sentence.
Hope this helped you out! :-)