Please refer to Wikipedia --"Simultaneous Interpretation" and "Consecutive Interpretation".
In (extempore) simultaneous interpretation (SI), the interpreter renders the message in the target-language as quickly as he or she can formulate it from the source language, while the source-language speaker continuously speaks; an oral-language SI interpreter, sitting in a sound-proof booth, speaks into a microphone, while clearly seeing and hearing the source-language speaker via earphones.
The simultaneous interpretation is rendered to the target-language listeners via their earphones.
The speakers and the audience will wear earphones while they are communicating. The interpreters stay in a booth/box/cabin where they speak through the SI receiving equipment, the interpretation takes place at the same time without interrupting the conversations, that is to say, the speakers do not need to give time for the interpreters to translate, they could speak continuously all day long without any barrier in different languages.
Usually there are two or more SI interpreters for an assignment, who will take turns to interprete every 15 minutes, unless it is a short whisper SI meeting which requires less intensive conversations.
It is medically harmful for the health of a SI interpreter if he/she undertakes a task all alone by himself/herself all day long.
Infrared facilities are needed for simultaneous interpretation tasks. Those facilities include the booths, interpreter's speaking machine and earphones, the listeners' earphones, infrared receiving equipment, etc.
For whisper interpretation, voice guide devices are necessary, unless the speakers stay in a quiet environment and are having one-on-one conversations without much external interference/noise.
In consecutive interpreting (CI), the interpreter speaks after the source-language speaker has finished speaking. The speech is divided into segments, and the interpreter sits or stands beside the source-language speaker, listening and taking notes as the speaker progresses through the message. When the speaker pauses or finishes speaking, the interpreter then renders a portion of the message or the entire message in the target language.
For consecutive interpretation and business entourage, one or more interpreters shall be assigned according to the intensity, duration and the scale of the conferences/trainings.
When the consecutive interpretation lasts for more than 2 hours, it is strongly recommended to hire at least 2 interpreters, who will take turns every 30 minutes.
You may like to watch the movie--THE INTERPRETER.
Or read my blog.
Peers in the translation industry are most welcome to contact me for interpretation opportunities (such as translation companies, relevant interpretation consulting companies, international conference organizers, simultaneous interpreters, etc.)
If you are from other entities or individuals, I will refer you to my appointed agency. For further information, please feel free to contact me.