Android, how to use the Accelerometer Sensors?

can someone help me understand the Accelerometer Sensor. I've read this and this overviews about the sensors and the motion sensor but i can't understand which movement triggers which sensor, (for an example the Sensor TYPE_ACCELEROMETER and Sensor event data SensorEvent.values[0] means Acceleration force along the x axis (including gravity).) what does that mean? which motion is it? So if anyone can help me, please all I want to know is to check if the phone is on a landscape orientation and standing vertically, and when the phone gets tilted to the front or backward. these are the 3 movements that I want to know, thanks