Gerber is a convention we use directly over No trump to ask for aces and kings. Generally, if you partner opens 1NT and you bid 4C this is Gerber and you should respond as follows: 

0-4 Aces -- 4D      1 Ace -- 4H       2 Aces -- 4S        3 Aces -- 4NT

If responder then bids 5C he is asking for Kings. Any other bid by him including 4nt is a signoff. Gerber can be used when partner bids 2C and then rebids 2nt or when he jumps to 2nt after he opened the bidding on the one level.  Caution:  When playing splinters an Unusual Jump to 4C is not Gerber.

Standard Blackwood also in a means we use to ask for Aces and Kings. A bid of 4nt asks opener for Aces.
These are the responses:

0-4 Aces -- 5C     1 Ace -- 5D       2 Aces -- 5H       3 Aces -- 5S

If responder then bids 5NT he is asking for Kings. To exitthis Blackwood the responder must bid a suit that hasn't been mentioned in the auction.  Roman Keycard Blackwood is a modification of Regular Blackwood and will be discussed separately.

You open the bidding 2nt.  With your partner hears this he is quite happy since he has a nice hand himself.

A jump to 4C is Gerber. 

Upon discovering that there are no missing Aces, your partner asks for Kings.  Your 5S bid tells your partner that you have 2 Kings. North can now confidently bid a Notrump Slam.