Could someone give an explanation of the use of the magnetometer of MUP9250，thanks
Have you looked at this?
The internet?
MPU
This discusses the MPU9250 and the AK8963 three-axis magnetometer.
But really, you should try some research before asking it to be handed to you.
i am so sorry to ask this question ,but i couldn't find the final code , 
"Final code" to do what?
Using the MPU9250 to get Real-time Motion Data | Arduino Project Hub in this site
he said the final code and i couldn't find it,