Multipath devices using

Hello everyone,
I read the document "Red Hat Enterprise Linux 5 DM Multipath". It say that when have new devices under the control of DM-multipath, the new devices may be seen in places: /dev/mapper/mpathn, /dev/mpath/mpathn, /dev/dm-n. Do not use /dev/dm-n and use /dev/mapper to access the multipathd devices. Who can explain detail about it, please ? If I use /dev/dm-n to create file system and mount it to a mount point, then how do it affect ?
Thanks,