Instructions
Turn off your Nintendo DSi.
Insert an SD flash card into the card reader on your Nintendo DSi console. Use the arrow on the card's label as a guide to make sure you are inserting it correctly. The arrow should point at the Nintendo DSi.
Turn on your Nintendo DSi. Select the icon for the game you want to play.
Play through the game until you are ready to save. Press "Start" and select the "Save" option. Select the SD card as a destination for the save file. A save game file will be created and placed on the SD card.