This series of tutorials will describe how to use some of the sizers that wxPython includes for managing widget location and resizing.
BoxSizerTutorial - A generic tutorial using only box sizers
GridSizerTutorial - A generic tutorial using a grid sizer
BoxSizerFromTheGroundUp - A detailed tutorial with working examples
GridBagSizerTutorial - A generic tutorial using a grid bag sizer
Other good sizer documents: