The way to put it would be that EQUALS and MATCHES are identical and do that same thing except MATCHES is intended for use when you also apply a (*) wildcard in your value. CONTAINS is different than MATCHES in that is that it will match on substring.
http://microsite.omniture.com/t2/help/en_US/analytics/segment/seg_operators.html
equals Returns items that match exactly for a numeric or string value. [Note: If using wildcard characters, use the "matches" operator.]
matches Returns items that match exactly based on a given numeric or string value. [Note: Use this operator when using wildcard (globbing) features.]
contains Returns items that compare to the substrings of the values entered. For example, if the rule for "Page" contains "Search", then it will match any page that has the substring "Search" in it, including "Search Results", "Search", and "Searching".
Best,
Brian