You communicate with it via hex commands through serial.
Play with the demo utility that came with it first and read through the documentation. Everything you need to get it working is there.
I recommend storing different commands as byte arrays ie:
uint8_t tagEPC2[] = { 0x0A, 0x51, 0x0D }; // Display tag EPC ID
// LF R 1 , 2 , 6 CR
// Not sure on this one
byte readmemepc[] = { 0x0A, 0x52, 0x31, 0x2C, 0x32, 0x2C, 0x36, 0x0D }; // Read tag memory data (EPC)
// Read EPC Address 2, 3 words
byte B[] = { 0x0A, 0x52, 0x31, 0x2C, 0x32, 0x2C, 0x33, 0x0D }; // Read tag memory data (EPC)
// Write envelope number to EPC
byte C[] = { 0x0A, 0x57, 0x31, 0x2C, 0x32, 0x2C, 0x33, 0x2C, 0x31, 0x37, 0x36, 0x30, 0x35, 0x33, 0x30, 0x30, 0x32, 0x30, 0x30, 0x30, 0x0D }; //
// Multi EPC
byte D[] = { 0x0A, 0x55, 0x0D }; //
// Single EPC [Q]
byte E[] = { 0x0A, 0x51, 0x0D }; //
That way you can effortlessly switch between different functionality, like leaving the module on constant read until it receives say a message from a webserver to go into write mode, etc..