Execute Query in Postgres Function

How do we execute a Query String in Postgresql function?
Or what is the equivalent of the following Code in MSSQL Stored
Procedure:

SET @QueryToPopulateTemp = "INSERT INTO
#Tmp_ConferenceDetail(ConferenceType, ConnectTime,
DisconnectTime,DestConversationId, Duration, AppConfId, OrigDeviceName,
DestDeviceName, destLegIdentifier) " + 
"SELECT  * FROM Tbl_Billing_Data ";        

EXEC sp_executesql @QueryToPopulateTemp;


Thanks for any inputs.

Regards,
Sumita