This command works simultaneously with the AdminServ FIELD command. Any FIELD added using AdminServ FIELD would then be SET using the /SET command. SET can either be used by a network operator or by a user, depending on the level of the FIELD you added.
/set Jennifer UserComment asks too many questions
If you are not using the web interface, the client might not understand this command, so use /quote set <nick> <field> <comment>. The fields are a good way to give people additional information about yourself. Remember to only provide information that you do not mind making public.