First of all, you had to know which device is going to asign for your pen drive. type this code after your plug-in your pen drive.
Then, you'll see the device of your pen drive is asign for. for example the device is asign for /dev/sdb.
Next, you have to decide which partition that you want to mount. if there're just one partition so it's should be /dev/sdb1.
And then, make a directory for your mount point. for example you'll mount to /mnt/penDrive.
The last thing before you run mount point, you have to know what kind of file system was used on your pen drive. for example, we assume the file system is FAT (16/32).
so, type this one to mount a pen drive to /mnt/penDrive where the file system is FAT.
mount -t vfat /dev/sdb1 /mnt/penDrive
Hope this information give you a view about your problem
Mardi V. Tamma