Survivors act as workers in the town either by stocking Products in Businesses, or by attacking Zombies in Supply Depots. Survivors show up at your front gate periodically, or you can also purchase them for Bucks (not recommended, since it's a total crap-shoot, as opposed to gate crashers who you can analyze first). You must have enough Housing slots to accept them in; if not, you'll need to either evict some people or build additional housing.
Each survivor has one of the following personalities:
Businesses and Supply Depots also have personalities, and if you match them together you get bonuses (50% more coins on products, 20% more supplies in supply depots).
A survivor's physical appearance will change depending on which personality they are. For example, Dreamers tend to look kind of spaced out, Realists look fairly deperessed.
Each survivor also has a level from 0 to level 9. These levels lead to discounts in the number of supplies required to create products. For example, a level 4, level 5, and level 9 survivor in each of the three product slots of a business will yield an 18% discount in supply requirements (4+5+9 = 18).
There is a way to increase the survivor skill level. This can be done by building a Survivor Dojo , which grants all survivors under that type an additional +1 to their skill level. Using a Dojo will allow you to reach a max level of 12.