How to calibrate ADC of STM32F334 Nucleo Board using STM32CubeMX code generator?

Hello, 

As I am working on analog inputs I require ADC. STM32F334 Nucleo board has 12-bit ADC (2) with 21 channels, I am using ADC1 Channel 1.

After programming without applying any input to the pin (PA0) I am getting some values through USART2.

Can anybody help me out.

Thanks in advance.