plug in your card reader (with a card in it) and type "dmesg". You should get a lot of text and in the few last line something like "gnagna new USB mass storage device... gnagna device XXX". (XXX = device name, most probably sda)
Then you could use "cfdisk /dev/XXX" to show partition on that thing.
Once you know the partitition number, just mount it :
mount -t vfat /dev/sda1 /where_you_want_the_thing_mounted
(note the vfat option is only if you use fat32 on your card).