What is the difference between assonance sibilance and alliteration?

All three are types of aural imagery which is probably the most prominent type of imagery as it is easily identified by reading out the text. It is spread into many sections. 

1) Alliteration: the repetition of the same consonant sound either at the beginning or into he middle of words. eg. perfect pike in all parts/ fragments of regret. 

2) Assonance: the repetition of a vowel sound either at the beginning or in the middle of words. eg. mighty cries in the night.

3)Sibilance: repetition of the 's' sound throughout a phrase or a sentence. eg. she slowly staggered across the street. 

 All three types of aural imagery may help to create a slower or faster rhythm or may aid to convey a certain feeling such as excitement (usually done with letters such as 'r') or sadness (usually done with 's' sounds). 
Remember: ALL ALLITERATION IS THERE FOR A REASON!