Search IUPAC Nomenclature
You know the name of a compound, say methylenedioxy, but do not know the structure of it. One of the easiest online way is to search for compound name in http://www.acdlabs.com/iupac/nomenclature/#search
Search for methylenedioxy resulted in following output:
A cyclic acetal in which the two acetal-oxygen atoms form part of a ring may be named: (a) as a heterocyclic compound; (b) by use of the prefix "methylenedioxy-" for the group as a substituent in the remainder of the molecule, derivatives of the methylenedioxy group being named as substitution products thereof; or (c) particularly when stereochemistry is implied in the name of the corresponding alcohol or ketone, as the alkylene or alkylidene derivative of that alcohol or as the alkylene or alkylidene acetal of that ketone.