By assonance we mean the repetition of a vowel sound with different surrounding consonants.For example:
So we'll go no more a-roving
by consonance we means a repetition of corrispondence of consonants without regards to vowels.For example:
Bare ruined choirs where late the sweet birds sang
by alliteration we means the recurrence of the same initial sound in words in close succession.For exemple:
Crossing the dead dull fields with footsteps cold
The rain drips drearily...