The css box model is is basicly a box that goes around every HTML element. it is made up of margins, borders, padding, and content. Its basicly a box inside anouther box
the main difference in margins and padding is that padding deals with innner space, margin deals with outer space inside the border.
you can set them to auto, which basicly the browser does it all and sees if it fits.
all it means is that the top and bottom padding is set to 25px and the right to left is set to 50px.