If your destination aiport is Boryspil, then you can get from the airport to the city by a bus: there's a special route called SkyBus, those buses stop just outside the exit from the airport. You can find more information here
https://kbp.aero/en/transport/sky-bus/If you are going on a two day tour you will stay in the hotel in Chernobyl, it is included in the tour's price. You don't need to book the hotel yourselve. All you need to do is to find a place where to stay in Kyiv before and after the tour