1stly you need to create a mount point under mnt eg perhaps call the mount point mp3 so do as root ( $ su and give the password) mkdir /mnt/mp3.
Next you have to determine the file system type of the partition you are going to mount lets assume its fat32 and its at hda3. You need to edit your /etc/fstab ( easiest is probably to use your desktop file manager) and add the line;
/dev/hda3 /mnt/mp3 vfat defaults,umask=000 0 0
You would have to reboot to get this established.
If you only wanted a temporary connection then as root do mount -t vfat /dev/hda3 /mnt