Labels (AKA tags) are used for grouping multiple agents into one logical group. Use spaces between each label. For instance 'regression java6' will assign a node the labels 'regression' and 'java6'.

For example, if you have multiple Windows agents and you have jobs that require Windows, then you can configure all your Windows agents to have the label 'windows', then tie the job to the 'windows' label. This allows your job to run on any of your Windows agents but not on anywhere else.