To follow on the topic of the difference between translation and interpretation, there are several kinds of interpretation in the industry. However, the two main kinds of interpretation are simultaneous and consecutive.
For simultaneous interpretation, the interpreter would have to verbally translate the message that the speaker is saying almost as quickly as how he or she can understand from the source language. This kind of interpretation normally occurs during a seminar or a large event whereby the target audience who needs the interpretation would be using earphones. The interpreter would normally be standing behind a sound-proof booth, so that his voice would not interfere that of the speaker.
In this case, it would be good if the client/speaker can provide reference materials for the interpreter to prepare the topic in advance, in order to also make sure the content is correctly delivered.
Sometimes 2 interpreters is necessary for this kind of job as it calls for much concentration and energy.
As for consecutive interpretation, the interpreter has ample time to digest or take notes of what the speaker is saying, then translate it out after the speaker has finished his sentence(s). This type of interpretation is not as tiring as that of simultaneous one. Of course it would still be good if reference material can also be provided. In this case the interpreter may stand beside the speaker during the seminar, and the audience do not need earphones.
If you know what kind of event your company is having, you can easily define what kind of interpreters you require, so that the interpreters know what to expect.