What should my very first cut be, and how do I know the machine passed?

Step 0: do not cut at all, draw

The canonical first run is a pen plot ("Hello World"): mount a pen (zip ties work, and some machines ship a pen mount) and plot a file on paper. You learn zeroing, job loading and running with literally zero risk. Ten minutes, huge confidence.

Step 1: the first real cut

A simple 3" circle or square in cheap scrap (MDF or pine), with conservative settings (about 1 mm depth per pass) and a hand hovering over pause. You are watching for correct position, correct depth, smooth motion, and nothing loosening.

Step 2: prove accuracy with three checks

1. Measure the circle or square with calipers and compare to the drawing. Off by a consistent percentage points to steps/mm calibration (see the calibration entry).
2. Circle-diamond-square test: the classic pattern exposes squareness, backlash and axis calibration in one part. The diagonals of the square must match, and the circle must be round, not oval.
3. Jog test: command a long known move (for example 600 mm) and measure actual travel with a tape. A machine that travels 602 mm needs steps/mm adjusted (most control software has a calibration wizard).

Hobby-class machines should land within roughly plus or minus 0.1 to 0.2 mm on these tests, which is plenty for woodwork. Chasing better than that comes later.

What NOT to do first

Do not make project one a hardwood heirloom, a V-carved sign, or anything with a deadline. The first ten cuts are tuition, so pay it in scrap (see the practice-materials entry).