The last component of a dialplan is the application – the action that will be performed on the current channel. We’ve already used the Dial application to dial a channel, but there are many more applications in Asterisk that enable you to do actions such as playing a sound, record user voice, queue a call, modify a database, etc.
Many applications require parameters in order to perform their job. These arguments are provided inside the parentheses after the name of the application. For example, the Playback application needs a filename of the sound you would like to play (e.g. Playback(tt-weasels)). The Dial application needs the channel and peer information (as in Dial(SIP/alice)). There are, however, application that work without any parameters, such as Answer or Hangup.