Layers can be grouped together for easier management and to restrict adjustments or masks to particular layers within your project. Layer groups can be nested together within a 'parent' layer group.
Grouped layers remain together so they can be easily selected, moved and copied. Furthermore, once a layer group is established, adjustments and masks can be applied to the group and will affect all the layers within it but not those outside of it.
Groups, and nested groups, can be broken apart at any time into their separate layers.
You can enable Ask for name when creating Layers and Groups setting to be prompted to name them upon creation. This is found in the Settings>User Interface section.