Through you computer? Just insert your usb cable into a usb port on your computer. Bring down your notifications bar, Then click "Usb connected" then click "Mount". You'll be able to access the SD. If this is what you are asking.
If you are asking about copying stuff from the phone to the SD card, Only way I know how is when you are rooted, You use root explorer or a similar program. Then you can have user rights and be able to save from the phone directory to the SD card.