All Survivors is the menu within the Armory where you can Compare, Retire, Upgrade/Inspect, Level Up, Evolve, and Favorite your Survivors. You can sort them by All, New, Level Up (will not be listed if you do not have enough XP), Leaders, and Subordinates. You can view them by description or their Personality, Leader Match (if they are a Leader), and Set Bonus (if they are a Subordinate).
Though mostly pointless, you can compare the descriptions of survivors. It will show which one has a higher Power Rating and Level.
Retiring survivors returns most of the XP put into them, or a small amount if they were not given XP. Survivors of Rare, Epic, Legendary, and Mythic rarity also give Training Manuals. Common and Uncommon Survivors do not give any Training Manuals.
You can view your Survivor's Rarity, Power Rating, Evolution Rating, Level, description, Personality, and Leader Match or Set Bonus. You can view your character's next Evolution Rating stats and requirements as well. Most importantly, you can level up your character using Survivor XP up to a multiple of 10 in which you are given the option to Evolve your Survivor, raising the Power Rating drastically.
Normally, Survivors that are in your All Survivors tab will be suggested in the Collection Book (it will make a number appear by the Survivor tab). By selecting Upgrade/Inspect, you can toggle Favorite. This will put this Survivor in front of all others (sorted by Power Rating) and hide them in the Collection Book. Even if you select that specific Survivor's Personality in the Collection Book, it will say "No items available" so you can never accidently slot your Survivor.