The beach stretches from the Hotel Bora Bora to Matira Point, which is a low sandy peninsula that juts into the lagoon. At low tide you can wade from here all the way out to the coral reef.
The only downside to Matira Beach is that it can get somewhat crowded and hectic, particularly on days when a cruise ship is docked nearby. Nonetheless it's still a beautiful (and free) attraction. In the evenings this west-facing beach is perfect for watching the sunset.