connect twc modem to mac air

I just had Time Warner Cable install internet service with my supplied Motorola modem. He told me all I had to do was connect the ethernet to my Mac Air and it would direct me to Time Warner Cable for setup. After the tech left I remembered that the Mac Air has only USB and Thunderbolt connections. So I went to Best Buy and purchased the Apple Thunderbolt to Gigabit Ethernet Adapter. I connected Ethernet cable from modem to purchassed adapter to Thunderbolt port and there is no direct to TWC website. Do I have the wrong adapter? I am sending this from Mac Air via personal hotspot on my iPhone5. Thanks for any help!!