Hi, and welcome to JA!
Punta Cana is part of the Dominican Republic (the far eastern tip of the island). It is a major resort area (the biggest being the "Punta Cana Resort").
Here is a map of the Dominican Republic, with Punta Cana circled in red (on the far right):
Here is a map of the half the Earth, with the Dominican Republic circled in red, to give you an idea of where in the world it is:
I hope this helps. Let me know if you have any questions, or need more maps.