Set photo stream to public?

What does it mean to set photo stream on my ios7 phone 4s to public? Can people I invite to their email view the stream also? Will Someone please explain how this works? Me and my sister were sharing an Apple ID for iTunes and I just learned I could create my own iCloud to back up my phone and still use the one we share for iTunes and other stuff on my 4s so now it reset the phot stream and I do not have it understood.