Compare the two? NFL Network is the single dedicated NFL channel, lots of news, talk, etc. Only live games shown on this channel are the Thursday Night games they televise. It is a regular channel included as part of your programming package. RedZone is an additional channel that is part of the add-on Multisport pack that only shows NFL programming on Sundays, and flips back and forth between games when teams are in the "Red Zone", and otherwise shows stats, highlights, etc.
On the other end of the spectrum...Sunday Ticket is the NFL's equivalent to MLB's Extra Innings or NBA's League Pass, where ALL games regardless of market are available each week on multiple dedicated channels. These all require add'l subscription costs. (I think I read the full price on DirecTV was like $360 for the season, though some get special deals to get it for less). The main difference is that MLB and NBA offerings are available on many different providers, including both Dish and DirecTV, but NFL Sunday Ticket is only available on DirecTV.