Well, your question isn't that clear to me, but I try:
Why?
* iOS is a derivate of Mac OS X, which is a derivate of BSD
* Using SSH you can change, view, copy, move files on your iOS device
* One of the best examples would be to change the SMS ringtones
* You need the SSH daemon running on iOS
How?
* In Cydia search for OpenSSH to install the SSH daemon
* SSH into your iOS device using PuTTY or similar program and change the root and mobile user passwords (default pwd is: alpine)
* If you're using SBSettings you should now have a new Toggle for SSH
