Google Sites is remaking itself to help websites look and function better with today's devices (ie. tablets, pads, smartphones, etc.). Website content will be more modular, thus easier to rearrange for device display areas.
Current (Classic) Sites websites need to be rebuilt in the (New) Sites environment (Get Started). Some of the Classic Sites features have not been set up under the New Sites tools, yet. Google will be adding features to the New Sites tools over the next year, or so.
Google Classic Sites will, eventually, be discontinued.