Like RoConno says, on a Dell Inspiron 1525, the Home button is the one that says "HOME" on it. It is to the right of the BACKSPACE button, above the PAGE UP button, and below the DELETE button- which is the button in the most upper right corner. It is marked "HOME".
As to what happens when you press the Home key, that varies with the application. It can be determined by either referring to the application's manual, or by actually pressing the button and observing the result. It should be noted that the Home key can be used in conjunction with other keys for different effects- ie Control + Home.