"Systems" are only going to be used for trunked systems; you'll only be using conventional programming on GMRS. You'll select conventional format from the Model Information page, which is accessed from the Model tab. In conventional programming, groups are just that - a group of channels. Inside the group, the channel up/down buttons will cycle between channels, while the group up/down buttons will cycle to a new group.
I have my GMRS radios programmed with a group or two for GMRS simplex channels, a group for GMRS repeater channels, a group with my specific local repeaters, a group with monitor-only ham frequencies, and one with FleetSync PTT ID enabled on GMRS simplex channels.