When a controller converts signals from your computer into motion, your machine will begin to move. You are now into the process of machining. Machining generally is cutting or removing of material. Most of the time we associate machining with metal, but you can also machine plastic or route wood. Working with wood or plastic is basically the same as working with metal, but faster.
To actually machine something you need a few different things. Since there are many things going on while machining you need to be aware of your safety. This is where the safety glasses come out and the personal protective gear is put on. Machining is a concert of movement, that requires many players.
Here are a few of them:
Machine - this could be a milling machine, plasma cutter, wood router, lathe or drill press.
Spindle - Most machines have one. This is the spinning portion of the machine. Like of the chuck on a drill, a spindle on a mill or a 3-jaw chuck on a lathe.
Tooling - This is the tool that does the cutting or removing of material. It could be an end mill, fly cutter, ball mill, etc.
Material - What you are going to be machining. What your part will be made out of. Steel, aluminum, wood, plastic, wax, etc.
Clamp or vice - imagine some material laying on a table and then you touch it with something spinning. Your material will instantly go flying and possibly hit you. This is why you always secure your material. This could be with a vise, clamp, bolt it down, gravity, suction, etc.
Cutting fluid - Some machining processes don't use cutting fluid. Plasma cutters and wood routers don't. Cutting fluid or coolant generally shows up when you are machining metal. The fluid is used to cool and lubricate the process which extends your tool life.
CNC - if you add CNC to the process you now have a computer, controller and cableing to worry about. Keep these things out of the way or protected while machining. Keep in mind a machine will be controlling another machine. This is the cool part about CNC and also where you can get into trouble.