Save Citizen
Citizens are poor, hapless residents of the cities found within Assassin's Creed that need saving. You can find their locations within cities by climbing to the tops of the View Points in that city and using your Eagle Vision ability.
These sad peasants find themselves in the unenviable position of being little more than toys of amusement for the corrupt town guards. What they did to upsets the guards varies. The citizens that need saving come in all shapes and sizes. Some are young women accused of stealing, some are monks, some were probably just in the wrong place, at the wrong time.
Either way, when you come across them, the poor citizen in question is being harassed by a group of guards. There are usually anywhere between three to five guards around the citizen. Two are in the process of actively shaking the citizen down while the remaining one to three guards stand as lookouts to keep the rest of the people in the area from trying to be brave and doing something foolish (like trying to stop them).
How you go about entering this sticky situation, and saving the citizen is entirely up to you. You can charge in, sword blazing away, or you can blend in and use stealth to get in close before beginning the killing. This way is handy as it allows you to get in at least one or two quiet kills with your hidden blade before the other guards notice what's going on. Or there's always the third option.....dropping into the middle of the group from the rooftops above and surprising the lot of them.
However you do it, once all of the guards are killed, you can talk to the citizen you just saved. They'll thank you profusely, and as a reward, a group of Vigilantes will now patrol that area and help you out if needed.