how does the reserve non football injury player rule work ?

I saw where the Saints put offensive lineman Avery Young on the reserve non-football injury list, so he no longer counts against the roster.

While I am happy it helps us in roster number count, how does that work ? how does he not count ? Will he be able to comeback anytime? or has to wait six weeks ? is like medical red shirt in college? kind of prevent other teams from claiming him?