A casting is an instance in which you need to look for a person to fill a specific role, whether in film, television, advertising, etc.. It is important to know that before the casting call and is predefined as the character, and the work of casting is to find the person best suited to that character. In some cases, the casting is not so strict and wanders between different possibilities.
Prior to casting personnel, there is a pre-selection is usually done by looking at the personal files of potential candidates, cv artistic pictures and sometimes videos. The photos are important because they are the first presentation, unless you have professional photos, avoid photos with family, friends, pets and all those who would rise to a photoblog, chances are you will not be taken seriously.
In a casting of action is to act and / or actors improvise different sequences that were previously sent to them or given a text to interpret at the moment. Many players often have little routines prepared to present, this is a plus if done right.
The so-called extras in many cases arise from a casting, is not always strict on this issue, but it is equally important since they are the atmosphere of the scene.
For all these reasons is that a casting is an important job and should be taken as such.