# = ids - these are unique can only be applied once per page (div id="header")
. = classes - these can be applied to several items on the same page, and can be combined (<p class="whiteText">, <a class="whiteText">, <p class="witheText bold">)
there is no sign before HTML tags (body, div, a, etc)
to have zero margins use in your CSS
body {margin:0px; padding:0px;}