Tiva C TM4C129 I2C Master implementation questions

Hello e2e folks-

I'm working on a simple I2C network with just two members, a Tiva C TM4C1294 launchpad and an arduino Uno. The Uno is acting as a slave and when prompted should return 4 2-byte variable values, and I think I have that working well enough.

So my problem is with the Tiva, I don't quite get how I2C works on this board, how to initialize it properly and request/receive values from slave devices.

I found this example code here-

#define ACCEL_SLAVE_ADDR 0x1D
#define XOUT8 0x06
#define YOUT8 0x07
#define ZOUT8 0x08
 
uint8_t ReadAccel(uint8_t reg)
{
    uint8_t accelData =  I2CReceive(ACCEL_SLAVE_ADDR, reg);
 
    return accelData;
}
 
void main(void)
{
    // Set the clocking to run directly from the external crystal/oscillator.
    SysCtlClockSet(SYSCTL_SYSDIV_1 | SYSCTL_USE_PLL | SYSCTL_OSC_INT | SYSCTL_XTAL_16MHZ);
 
    //initialize I2C module 0
    InitI2C0();
 
    uint8_t Ax, Ay, Az;
 
    Ax = ReadAccel(XOUT8);
    Ay = ReadAccel(YOUT8);
    Az = ReadAccel(ZOUT8);
 
    while(1){};
}

I see that it's setting XOUT8, YOUT8, and ZOUT8 to read values from I2C, and sending seemingly arbitrary numbers as the "reg" argument in the ReadAccel function. I don't understand how that correlates to requesting the data from those registers and what exactly accelData has as a value after reading in bytes. Is it the last value that the slave sent?

In case I'm making things more difficult for myself, I'm just trying to send 4 2-byte variables from the arduino slave to the tiva master, if there's an easy way to do this I'd love any suggestions you guys might have.

Thank you

Garrett