A CNC part program is an ordered set of commands that tells a controller how to prepare and execute machining motions.

Although exact syntax varies by controller, programs commonly express the same ideas:

• select a tool and its offset;
• choose spindle speed and direction;
• choose feed rate;
• move rapidly to a safe approach point;
• perform controlled cutting moves;
• call repeated machining cycles when useful;
• stop or change tools safely.

A simplified sequence might be interpreted as

select drill
start spindle
move above hole
feed to hole depth
retract
stop spindle

A real program must also make its modal state unambiguous. A modal command remains active until changed, so a feed mode, coordinate mode or motion mode can affect later blocks without being repeated.

Repeated operations can often be represented by canned cycles or subprograms. For example, drilling ten holes should not require rewriting the entire approach-feed-retract logic ten times if the controller can apply one cycle at ten positions.

Safe programming requires reasoning about more than final geometry. Rapid moves need clearance; tool changes need safe positions; spindle and coolant state must match the operation; offsets must correspond to the installed tool.

The central idea is that CNC programming converts intended machining operations into an executable sequence of machine states and motions. It is not merely a list of coordinates.