The following information was found on the EBU website and in the instructions how to use bidding boxes:
Bidding Box Usage
Starting with the dealer, players place their calls on the table in front of them, from the left and neatly overlapping, so that all calls are visible and faced towards partner. Players should refrain from touching any cards in the box until they have determined their call. A call is considered to have been made when it has been removed from the bidding box with apparent intent (but the director may apply Law 25). Note that some left-handed bidding boxes are available, where the calls are placed in a row from right to left.
Hesitation between bids, when touching the bidding cards, is liable to penalty as unauthorized information.
Alerts
Alerts should be made by use of the Alert card. It is the responsibility of the alerting player to ensure that both his opponents are aware of the alert.
The Stop card
Before making a jump bid (i.e. a bid at a higher level than the minimum required) a player must place the Stop card in front of him, then place his call as usual, and eventually remove the Stop card. His left-hand opponent should not call until the Stop card has been removed. The Stop card should be left on the table for about ten seconds, to give the next player time to reflect. It should not be removed prematurely.
After a jump bid, the next player must pause for about ten seconds before calling. It is an offence either not to pause or to show indifference when pausing. If the Stop card has been removed prematurely or has not been used, an opponent should pause as though the Stop card had been used correctly.
End of the auction
At the end of the auction the calls should remain in place until the opening lead has been faced and all explanations have been obtained (this is equivalent to the right of every player except dummy to have the bidding repeated before the first lead), after which they should be returned to their boxes.
Change of call
Calls made using cards are treated under the Laws in the same way as spoken calls. For example, a call may be changed without penalty under Law 25A only if: