Civilians are just like you: Average people caught up in the zombie apocalypse. They will be both allies and enemies, allying with you to combat the undead horde and killing you for scraps of food. Civilians can get quite self-dependent if they survive long enough to get good skills.
On their ownEdit
Civilians are, by default, not hostile to you. They will combat the undead intelligently, attacking then retreating, but are very vulnerable to hordes. You will often see Civilians following a Cop, or following a fellow Civilian who has the Leadership skill. If they have free inventory space, they will rush towards the nearest item they can put to use, mainly food, weapons, and medical supplies.
You can trade with any Civilian by merely walking into them, or hovering over an item you want to trade and pressing e. They are an excellent source of getting more food via trades, and will commonly accept medicine, flashlights, and cell phonex in exchange.
They can survive well enough on their own, depending on what equipment they have acquired. A survivor with an improvised spear won't last long without assistance, while one with a hunting rifle and some ammo can last quite a while. They will put themselves before you if they have to though, but more on that later.
If you have at least 1 point in the Leadership skill, you can recruit a non-hostile Civilian with T. They require food and sleep just like you, so make sure you have extra supplies and a bed or two in your safehouse. However, they also bring numerous advantages. They have their own inventory, and their AI is anything but stupid. Once Trust is at maximum you can give orders to them, such as staying to guard your safehouse, sitting in a certain position, giving you items, or relaying news they have heard in your absence.
If you can afford their food and sleep needs, there is no reason to not get a companion. A companion with decent skills will vastly improve your survival odds, and can guard your safehouse while you're away, and protect you while you're sleeping. If they have planks in their inventory, they will also reinforce and create barricades and fortifications themselves.
Civilians will become your enemies under specific conditions. The most common one is hunger. A civilian whos hunger bar is at half or lower and cannot find any food will begin assaulting anyone who holds food to get it. You can avoid this by dropping food then running away before they hit you, but once they strike you they will attack until you're dead.
Hungry civilians will also actively destroy weak barricades, which can be a huge problem when you're asleep in your safehouse. A survivor will beat down your barricades, search the house for food, kill you in your sleep if you have any on you, and promptly leave. They are rather deterred by full-strength barricades however.
Your only choice is to either kill them, which as of alpha 6 will be labeled as a 'murder', or flee. If a Police Officer spots you getting assaulted he and his companions will aid you. It's often best to just avoid any hungry survivors you see, and if you're wounded just give them something to eat to avoid unnecessary death.