You've already set foot on the coast of sunny Greece, but that's not all. You need to get to Kefalos from Kos airport. The resort is just 15km from the airport.
Optionally, you can take public transportation. The bus follows the route from Kos town through the airport and to Kefalos resort (namely to the stop of Tsooukalis supermarket). The fare is 4 EUR. You can check the exact schedule here.
An alternative to taking public transportation is to call a cab. You'll spend much less time on the road: about 10-15 minutes, but you'll have to pay around 40 EUR. If comfort is your priority, you can book a car in advance at this site, even if you have to pay to call a cab over the phone.
You can also get to Kefalos in a rental car. There's only one road, so it's hard to get lost. You can find a car at the following resource. Expect to pay from 40 EUR per day.