After opening 2NT bid, 3S is one of three types of minor suit try:

    -- Both minors, 5-5
    -- Single suit clubs
    -- Single suit diamonds

If opener has no 4-card minor, or poor hand/controls, they bid 3NT.
Responder continues:

        4C -- single suited slam try, clubs
            opener continues:
                4D -- key card
                4H,4S -- cues
                4N -- suggestion to play, either poor trumps or poor controls. 
                5C -- cue in D
        4D -- single suited slam try, diamonds
            opener continues:
                4H -- key card
                4S,5C -- cues
                4N -- suggestion to play, either poor trumps or poor controls. 
                5D -- cue in H
        4H -- 5-5 minors, singleton H, 
            opener continues:
                4S -- slam hand in either
                4N -- suggestion to play
                Can bid game, slam, or cue
        4S -- 5-5 minors, singleton S
            opener continues:
                4N -- suggestion to play
                Can bid game, slam, or cue
        5C -- long C suit, not greatly slammish but 7+ cards
        5D -- long D suit, not greatly slammish but 7+ cards

If opener has 4-card minor and good controls, they bid the minor (C with both).

    4C -- opener has good hand, 4 clubs
            
        Responder continues:
            4D -- key card
            4H -- singleton with clubs
            4S -- singleton with clubs
            4N -- one suit, diamonds, willing to play 4NT
            5C -- club one suiter, no shortness and can't make slam bid
            5D -- diamonds, one suit, not willing to play 4NT

    4D -- opener has good hand, 4 diamonds
            
        Responder continues:
            4H -- key card
            4S -- one suit, clubs, slammish
            4N -- one suit, clubs, willing to play 4NT
            5C -- club one suiter, not willing to play 4NT
            5D -- diamond support, not real good hand