gray cards/white balance cards

So i was just wondering what these are used for and actually how you use them? i know they are used to adjust for white balance but i am not sure how to use them... Thanks!

Do a search you will find a lot of info on this.

Also the manual will tell you how to set a custom white balence in the camera with a white or gray card. It's good to do for each shooting situation. However this is not practicle at times... So you shoot a picture of the gray in the frame. Then use it to set the balence as you are working on the image during post processing.

Sticky: Photography Links

o thanks for the stickey! i looked everywhere except the talk about photo ><

you might also google expodisc if you're thinking about manual white balance.