A simple bluetooth module like a HC-05 wired to your Arduino will give you a serial stream that can be read and/or written.
With the RX/TX connected to say pins 10 & 11, a SoftwareSerial() object will provide access:
#include <SoftwareSerial.h>
SoftwareSerial mySerial(10, 11); // RX, TX
void setup()
{
mySerial.begin(9600);
}
void loop()
{
int value;
if (mySerial.available(sizeof(int)))
{
value = mySerial.parseInt();
}
}
If you connect the module to pins 0 & 1 - you can just use the Arduino standard Serial functions, but it will cause problems uploading to the board. In which case you would disconnect the bluetooth module for uploading.