"Open-jaw" simply means the airport you land at is not the one you fly home from. On the Turkish coast the natural pair is Antalya and Dalaman: two airports at either end of the same stretch of shoreline, with very different holiday areas around each.
A typical shape looks like this:
- Arrival: land at AYT and transfer to your first hotel, for example in Belek, Side, Lara or Kemer.
- Hotel change: after a week or so, a private car drives you west along the coast to Kaş, Kalkan, Fethiye or Ölüdeniz.
- Departure: from your second hotel to Dalaman Airport, and home.
The point is to avoid doing the long coastal drive twice. If you flew in and out of Antalya, a week in Fethiye would mean the same long road back on your last morning.