Basically, redemption is collective and salvation is individual. By his passion, death, and resurrection, Christ redeemed humanity collectively from slavery to sin and from the debt of punishment mankind – as a whole – owed due to sin. Each and every person, Christian or non-Christian, is redeemed because he is a member of the human race.
Salvation is the application of redemption to individuals. Although a member of redeemed humanity, and therefore himself redeemed, a person can freely choose to deliberately reject the graces won for him by Christ and go to hell.