Administrators can enable or disable tags on the Configure global agent options tab under System setup.
When Tags are enabled, agents can tag their calls. This can be useful to categorise calls and filter them in the Tags Report.
When the agent is on a call, there will be a tab with a label icon on the Navigation panel on the right hand side (as shown below), which allows the agent to tag the call from pre-set tags (managed in the configuration panel):
Once this is done, the agent should click the tick icon to disposition the call when it is completed.