Before plug in USB pen see /var/log/messages kernel through which you get device name and path. Here I get sdc as device name (or sda0, sda1 like that.).
Now mount it.
Mount for FAT file system
mount –t vfat /dev/sdc /mnt/mounttemp/
Mount for NTFS file system
mount –t ntfs /dev/sdc /mnt/mounttemp/
access your device
