First of all i assume you do have a datasheet and reference manual. I you don't have those get it from Resources page.
1) For any pirephiral you need to enable clocking. All GPIOs are allready clocked by CircleOS for use with MEMS sensor, display & other. If you don't use CircleOS you will need to do that manualy (code for different libraries):
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOC, ENABLE); //Using ST-LIB
RCC->APB2ENR |= RCC_APB2ENR_IOPCEN; //Using CMSIS
2) Configure GPIO as analog pin.
//ST-LIB
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_4 | GPIO_Pin_5; //Ext. connector 11,12
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AIN;
GPIO_Init(GPIOC, &GPIO_InitStructure);
//CMSIS
GPIOC->CRL &=~( GPIO_CRL_MODE4 | GPIO_CRL_CNF4 );
GPIOC->CRL &=~( GPIO_CRL_MODE5 | GPIO_CRL_CNF5 );
3) Enable ADC clock:
RCC_APB2PeriphClockCmd( RCC_APB2Periph_ADC2, ENABLE ); //ST-LIB
RCC->APB2EN |= RCC_APB2ENR_ADC2EN; //CMSIS
4) Then you need to configure ADC2.
Can't help you any further because i'm using CMSIS library and it's not suitable for novices. It's probably not the best idea to use CMSIS for your code.
