Many clubs, and some home players, use bridge bidding boxes. If you use these then you make your bid by displaying the relevant cards, rather than speaking it out loud. This has obvious advantages in a large club, where spoken bidding could be distracting to players on other tables. It also means that, even in a social situation, everyone is clear what your bid is. No mistakes from mishearing.
Each box contains a set of cards, with one card for each possible bid.
When a player makes a bid he places the relevant card (together with all the cards behind it in the box) on the table. Every player can see the bid without any words having to be spoken.
When the bidding has finished the player gathers up the cards and replaces them in the box.
The box also contains extra cards which are used for special functions such as passing and doubling. There is also a stop card which is used before making a jump bid and an alert card which you use if your partner makes a bid that has a special meaning for your partnerships - for example if you are using Stayman or Blackwood.