Not very much in practice, as they come up with "Onde vão as suas irmãs" Where are your sisters going?" when it should be "Aonde..." Aonde" is a + onde, to be used where there is movement towards somewhere, Onde when the action is static. As my old schoolfriend David points out above, English had a word, like aonde, meaning "to where" = "whither". That is not used nowadays. In the same way Portuguese has "donde" which is de+ onde, meaning "from where" and the English word was "whence".