programming a PIC using c language

hai i am very new to pic programming using c language.... i got a few set of lines from the web and am finding it hard to understand them..... i am hoping that someone can explain to me this lines..... i am trying to built a elevator system using pic16f877....

// the push-buttons that request the elevator target floor
// we map BUTTON_0=RA4 etc. to keep the schematics simple..
//
#define BUTTON_0 RA4
#define BUTTON_1 RA3
#define BUTTON_2 RA2
#define BUTTON_3 RA1
#define BUTTON_4 RA0

// the sensors that indicate which floor the elevator car
// has reached. Again we map 0-4 1-3 etc. to avoid signal
// crossing in the schematics.
//
#define SENSOR_0 RB4
#define SENSOR_1 RB3
#define SENSOR_2 RB2
#define SENSOR_3 RB1
#define SENSOR_4 RB0

// two output ports used to control the elevator motor
// (on/off) and motor direction (up/ndown).
//
#define MOTOR_ON RB6
#define UP_NDOWN RB7

// the elevator states: parked means waiting (at floor < i >),
// up_to and down_to imply moving to the corresponding floor.
// We force an encoding that allows you to watch the state
// during the simulation (upper nibble=1/2/4: parked/up/down),
// lower nibble=floor index, 0xff=error
//

//I DONT UNDERSTAND FROM THIS LINE

enum elevator_state {
PARKED_0 = 0x10,
PARKED_1 = 0x11,
PARKED_2 = 0x12,
PARKED_3 = 0x13,
PARKED_4 = 0x14,

UP_TO_1 = 0x21,
UP_TO_2 = 0x22,
UP_TO_3 = 0x23,
UP_TO_4 = 0x24,

DOWN_TO_3 = 0x43,
DOWN_TO_2 = 0x42,
DOWN_TO_1 = 0x41,
DOWN_TO_0 = 0x40,

UNKNOWN = 0xff,
};

enum motor_state {
STOP = 0x00,
MOVE_UP = 0xc0,
MOVE_DOWN = 0x80,
};


// global variables for state-machine state and motor control
//
unsigned char state = PARKED_0;
unsigned char motor = STOP;



// inidicate an error by lighting the LED on port B.5
// (note that RB5 is also used to reset the SR-flipflops,
// but the short strobes should not be visible on a real LED.
void
error(void)
{
motor = STOP;
for(; {
RB5 = 1;
}
}