Grouping layers is effectively placing layers under a parent layer. The child layers will inherit the properties of the parent layer, but also keep their own individual properties.
Grouping layers is as easy as dragging and dropping the layers you want to group, onto a parent layer. This parent layer acts as a container.
In this example, we have 3 individual colored tiles:
To make the container layer, make a new layer and rename it...
...scale it to the fit around the colored tiles...
...and set the fill color the transparent.
Now just drag the layers onto the container, in the layer list.
Now you can move and animate the group as a whole by applying properties to the "container" layer.
Layers can be ungrouped by dragging them out from under the parent layer and dropping them between two other layers.