CNC stands for "computer numerical control." A CNC machine is simply a machine whose movement is controlled by a computer. A CNC router is a machine that can route, mill, surface, drill, groove, saw and polish depending on the model and manufacturer. Each operation needs only a different tool and those tools' operating parameters. Most CNC machines available today offer an "automatic tool changer" whereby the machine can change the tool by itself without manual intervention. That means if you type "T1" into the control, the machine will return whichever tool it is currently holding to its own tool position before going to pick up Tool #1. How many tool positions a machine has varies by vendor and model. For instance, the Brembana Maxima can have a 22-, 26-, or 44-position tool rack.
Programming for these machines is accomplished using software, and each year the software gets better and easier to use. Most CNC machines that use industrial controls have had flexibility and reliability designed into them, but driving the machines with little or no software can be at best trying. In a recent development, CMS Brembana is working with a technology company to use digital imaging in place of manual templating, which means, instead of making a physical template, one can just take a series of digital photos in the field, and the CNC programs can be made from this data using only software.