Well there are ways to do it directly on the tablet, however they usually take a while due to having to move one file at a time.
However, to make it much quicker, you can hook up the tablet, via USB cord, to a computer. Then move all the files you wish to put on the card into an empty folder on the computer. When they are all on the computer, then you can (using the same USB connection) copy them all over to the card. Once you are done, be sure to reboot the tablet.
NOTE: This will only work with photos, music, videos, etc. Not with apps.