I found something:

1. STM 32 has an internal oscillator, so no need extra oscillator to make it work. And also, if you stuck in an external oscillator, you have to config your stm32 to use, otherwise it will just use internal oscillator
2. You just need 4 pins to make it work. 3.3v + GND + SWCLK + SWIO to burn something into your stm32. So STM32 is as raw as AVR.