Let suppose you are trying to segment a list of product names which include -
prod1, prod2, prod3, prod4, prod5
in segment builder if you put product name contains 'prod' the result would be - prod1, prod2, prod3, prod4, prod5
and if you put product name equals 'prod4' the result would be - prod4
so in essence 'equals' gives an exact match and 'contains' pulls the whole string which contains the said expression
Hope that helps.
Tanmay