I can't get back to my MAC Operating system!?

I just got started with the installation of windows 10 to my Macbook Air and when I reached the place to select a partition then I deleted the partition and made a new partition

And after the completion of windows installation I can't head back to the Mac designed OS.

Its like that with the partition deletion process the Mac OS is gone.

Any way how I can reinstall it somehow get back to the Mac system

Id not want windows just screw windows I want my own lovely Mac OS

Any way?