#Step: 1> Download STM32 Hardware file to support STM32 board for Arduino IDE software. You can download from here STM32_Hardware.
#Step: 2> Extract this file and copy files to the Arduino hardware folder.
#Step: 3> Now, Copy libraries for STM32 to the Arduino libraries folder to get all the sample programs in your IDE software.
#Step: 4> Open Arduino IDE software. Go to Tools -> Boards -> Board Manager
After selecting board manager you will find out following window.
Install Arduino SAMD Boards (32-bits Arm cortex-M0+) by Arduino and restart Arduino IDE Software.
#Step: 5> Connect your device to computer and select your board from tools as shown in following picture.
After selecting board now select communication method and COM Port,
Now, You can program this board as per your Applications.