4NT asks for the number of Aces and King of Trumps (5 Keycards). Trumps are either agreed or the last bid suit.
The responses are:
5♣ 1 or 4 keycards. (14! - why named 1430)
5♦ 0 or 3 keycards (30!)
5♥ 2 keycards without the Q of trumps
5♠ 2 keycards and the Q of trumps
Normally (about 75% of the time) it is the stronger bid that asks for keycards.
5NT asks for Kings (except the King of Trumps). Only done if asker has checked that all keycards are held by the partnership.
0 Kings bid 6 of trumps
1 or 2 Kings bid 6 of the lowest K held.
3 Kings bid 7 of trump suit.
If the response of 0 or 1 keycards you may need to find the Q of trumps.
So if after
4NT - 5♣ C (showing 1 or 4 keycards)
5♦ (Next bid up) asks for Q
No Q bid 5 of trump suit
Q but no K bid 6 of trump suit
Q but a K bid the lowest K e.g. with K♣ s bid 6♣
If the K is above the trump suit, bid 5NT
More Information Here.
This includes good examples and why 1430 version is better.
Beyond the first 4 responses it is possible to also show "useful" voids. The definition of useful voids is a void that could be useful, either a void in a suit bid by the opposition or a suit not bid by your partnership. A void in one of partners suits is not likely to be useful.
5N - Even number of keycards + a useful void
6♣ - Odd Number of keycards + a useful void