From calm little bays to...
In Puerto Escondido you can take your pick of beaches: little bays with calm waters for swimming like Playas Manzanillo and Carrizalillo, or even Playa Principal (if you don't mind the crowds and the boats). Or long and wide windswept beaches with pounding waves for surfers, like Playa Zicatela.
The climate is tropical (hot and humid), so you ought to keep yourself near the ocean or the pool, or risk melting into your sandals! And this is especially true at mid-day.
PE is a laid back town where Mexicans vacation with their family and fishermen still go out fishing in the morning (and give boat tours to tourists in the afternoon).
It's not Cancun, but it's definitely not undiscovered! Fortunately prices are still at Mexican (not international) levels, and that means you can rent a beach chair for $2 for the whole day.
There is a good selection of restaurants and many shops selling handicrafts and beach wear on the main (tourist) drag: Perez Gasga. Some visitors spend several weeks here, so they may need to build a wardrobe I guess... bikinis, sarongs, sundresses... :-)