You should find a better translator. Try google translate. Many of us are not native English speakers so your poor English is really not helping us understand what you want.
I guessed what you want is to capture X and then A from serial port and do something when this happens.
You have a loop, the loop() function to loop around while you check for X. That works. You need another loop to check for A:
void loop()
{
char in_byte=0;
while (!serial.available()) //Wait for incoming character
{}
in_byte=Serial.read();
if (in_byte=='X')
{
while (!serial.available()) //Wait for incoming character
{}
in_byte=Serial.read();
if (in_byte=='A')
{//Do your X then A action
}
}
}