Well yes it's kind of self-explanatory in the sense of flashing, however the part that I'm unsure of is why the OP said do the same on boot_a and boot_b? I don't get it. Do I also do the same?Pretty self-explanatory
boot_10s.img = stock boot image
boot_10s-magisk.img = has root
fastboot flash boot_a boot_10s-magisk.img
then
fastboot flash boot_b boot_10s-magisk.img
Sorry if this question seems very easy, I'm still learning, it's my first root attempt.