You can set up a personal presence status showing whether you’re available to talk or you’re busy. To change your status, simply click on the little dot at the bottom of your userpic:
Call handling options
This presence status can be used to define how your incoming calls will be handled in Settings > Answering Rules. First, an audio recording will be played (it can be disabled by clicking on the gear icon in the upper right corner of a greeting block):
If your status is set to Do not Disturb, calls will disconnect or go to voicemail;
If your status is set to Busy, calls will disconnect, get put on hold / sent to call waiting or go to voicemail;
If your status is set to No answer, calls will disconnect or go to voicemail.
Click on the wheel icon in the upper right corner of each block below to select the desired option: