Support refers to the scaffolding material that breaks off of a print required for extreme angles. Since prints build layer by layer, the filament needs something to be laid upon without the material drooping. Each material requires its own support settings and have their own angles that can be printed without support.
As mentioned in the Orientation of Print section, support material is needed for extreme overhangs. The angle at which the printer will generate support material is chosen within the slicing program. The amount of material (fill) generated in the support can also be chosen. When using dissolvable support and dual extruders, you are able to take the angle down to 0° and fill up to 100%, causing the printer to create a solid block of support material. The higher the percentage and lower the angle, the longer the print and more material that is required. This is why it is beneficial to design parts that require the least amount of support. The distance from the print in the XY and Z directions refer to the amount of space between the print and the support material. The closer the material, the cleaner the underside of the overhang, but the more difficult the support is to remove.
When printing with a single extruder these settings will have to be tweaked depending on the material used. PLA can handle angles as high as 55° or 60° and only requires a 15% support fill, printing at a distance of .8mm in the XY directions and .16mm in the Z direction. ABS, on the otherhand, requires a higher support fill of 23% and is required at 45° and above. The distance from the print should be .7mm in the xy direction and .13mm in the z. These settings will be tweaked depending on your printer and extruder. Some materials just cannot print support and have a successful clean print, making the design of the model that much more important.
One frustrating part about 3D printing is support removal. With settings drastically closer and in a higher support fill than those described above, you will often need to resort to sanding machines and time consuming labor. Removal should be fairly easy on PLA and ABS with a set of pliers, but even with the best settings the print will be cleaner without the markings of removable parent support material.