Google maps search "Finikia Parking Area"  There are two main roads to reach Oia, the parking lot of Finikia is located as you reach the village. If you choose the beach road (new road), when you see "Laze pool bar"on the right, and a big road on the left, make a left hand turn onto the road, drive for approximate 1,3 kilometer and you will see the parking lot on the left hand side.
Please note if you use a GPS don't follow the quickest rute it will pass you from an old road without asphalt. It will be better if you search for "laze beach bar" in your GPS.
If you choose the mountain (old road), when you see “Oia Suites” on the left, and restaurant “Santorini Mou” on the right, make a right hand turn onto the road just past the restaurant. Proceed downhill 80 meters and you will see the parking lot on the right hand side.