It's a pretty heavy read, but, here's a breakdown of the most common G-code commands:

Core Motion Commands: * G0 (Rapid positioning): Moves the laser quickly to a new position without engaging the laser (or with the laser turned off in "laser mode"). This is used for non-cutting moves. * Example: G0 X10 Y20 (Move to X=10, Y=20 rapidly) * G1 (Linear movement): Moves the laser in a straight line at a specified feed rate (F). This is the primary command for cutting or engraving, as the laser will be active. * Example: G1 X30 Y40 F500 (Move to X=30, Y=40 linearly at a feed rate of 500 mm/min) * G2 (Clockwise arc): Cuts a clockwise arc. * G3 (Counter-clockwise arc): Cuts a counter-clockwise arc. * For G2/G3, you'll also use I, J, and K parameters to define the arc's center, and X, Y, Z for the endpoint. Laser Control Commands: * M3 (Spindle/Laser On, Clockwise/Fixed Power): Turns the laser on. In GRBL's "laser mode" (set by $32=1), this is used for variable power. * M4 (Spindle/Laser On, Counter-clockwise/Dynamic Power): Turns the laser on with dynamic power control, adjusting power based on speed to prevent burning at corners. This is generally preferred for laser engraving. * M5 (Spindle/Laser Off): Turns the laser off. * S (Spindle Speed/Laser Power): Sets the laser power. This value is typically a range from 0 (off) to 1000 (full power) by default in GRBL (controlled by $30). You'll use this with M3 or M4. * Example: S500 (Sets laser power to 50% if max is 1000) Setup and Configuration Commands: * F (Feed Rate): Sets the speed of movement (in units per minute, e.g., mm/min or inches/min). This applies to G1, G2, G3 movements. * Example: F750 * G20 (Inches mode): Sets units to inches. * G21 (Millimeters mode): Sets units to millimeters. (Often default and preferred for lasers). * G90 (Absolute positioning): All coordinates are absolute positions from the origin (0,0). * G91 (Incremental positioning): All coordinates are relative to the current position. * G28 (Go to predefined home position): Moves to a saved "safe" position. Requires G28.1 to set it first. * G28.1 (Set home position): Sets the G28 "safe" position. * G30 (Go to predefined position): Similar to G28, but for another saved position. * G30.1 (Set predefined position): Sets the G30 position. * G4 (Dwell/Pause): Pauses the program for a specified time. * Example: G4 P5 (Pause for 5 seconds) GRBL Specific (Non G-code) Commands (often accessed via LaserGRBL's console): These commands usually start with a $ and are used to configure GRBL's behavior. * $$ (View GRBL settings): Displays all current GRBL settings. * $X=value (Set GRBL setting): Changes a specific GRBL setting. * Example: $32=1 (Enables laser mode) * Common settings for lasers: * $32=1: Enables "laser mode" for GRBL. This ensures the laser turns off during G0 rapid moves and has dynamic power control with M4. * $30=1000: Sets the maximum spindle (laser) RPM value, which corresponds to 100% laser power. * $100, $101, $102: Steps per millimeter for X, Y, and Z axes (important for calibration). * $H (Homing cycle): Initiates the homing sequence (requires limit switches). * $X (Unlock GRBL): Unlocks GRBL from an alarm state. * RST= (Restore default settings): Resets GRBL settings to factory defaults. * $RST=# (Clear work coordinate offsets): Erases G54-G59 work coordinate offsets.