Control CNC robotic arm - GRBL (integration of inverse kinematics)

Hello community Arduino, I'm working on a printable robotic arm zortrax consisting of 3 engines Nema step 17 for the first three joints from the base and a microservomotor for the 4th, where will the tool holder arm, will be controlled by an Arduino UNO and CNC gRBL shield with their respective driver 4988 for engines, found the library grbl grbl/grbl at master · grbl/grbl · GitHub which is made as firmware that once loaded on the Arduino board You could receive orders from the "Universal Gcode Sender" software.
My doubts are based on the following, I studied that in order to place the tool tip of the arm (which I shall place the extruder creams or filaments or pencil or mototool) in the desired workplace place to carry out the orders received in series according to the coordinates of the G-code, we need to implement inverse kinematics, and not even, I do not have enough understanding of the subject to come up with the solution, any of you could help me answer this question? And my arm to make effective tool for machining multitasking desktop? Thank you !!!

any of you could help me answer this question?

What question?

GRBL is used to send M and G codes to the Arduino which, in turn, makes the motors move in the appropriate way.

You need some application on the PC that creates M and G codes that will cause the moved objects (arms) end up in the correct place.

If you want to make the end effector on the robot move to specific X, Y, Z locations, that is where the inverse kinematics comes into play, working out the joint angles needed to put the end effector in that location.

Frankly, I do not think that you are ready to be marketing a useful system yet. You have a lot to learn, still.

The inverse kinematics for a 3 DOF robot is not that hard: