Help triggering sound from SD card

can anyone please help on how to trigger one single wav file from a sd card. Code would be very helpful.
I use the Arduino 328 board and attached the waveshield 1.1 kit (with SD card slot) on top.

It sounds like you have the Wave Shield from Adafruit. Have you tried the examples for that shield at Audio Shield for Arduino? The most simple ones are at the heading "Digital audio player" on that page.