Used to replace words of a sexually indecent nature. Usually words that are racy or risque. Could be used to replace any word you wish, to create a double entendre. Similar to saying after any sentence, "If you know what I mean." Just to hint that you intended to sound dirty.
An expression used in response to a request for attention, equivalent to "Yes, how can I help you?" or "Oh, hello, do you have something you wish to converse with me about?".