Playing a group in the audio manager is as simple as playing a clip like so:

// Standard group play from the library...
AudioManager.PlayGroup(Group.MyGroupName);

// Standard group play without being defined in the library...
var clips = new string[3] { "Click_01",  "Click_02", "Click_03" };
AudioManager.PlayGroup(clips, GroupPlayMode.Random);

Groups are setup in either in the library editor or by passing in a collection of strings and defining one at runtime. The setup is identical to the clips setup otherwise with the same overrides where applicable and the same volume and pitch edit variants as well as the fully edit module setup should you need it:

AudioManager.PlayGroup(Group.MyGroupName, new VolumeEdit(1f), new PitchEdit(1f));