Use $main, $help_section and $page_data and define css style "current" or wnatever you want to call it
{if $main eq "...."}, {if $help_section eq "contactus"}, {if $page_data.pageid eq "...."}
Something like this
<a href=""{if $help_section eq "contactus"} class="current"{/if}>Contact Us</a>
<a href=""{if $page_data.pageid eq "5"} class="current"{/if}>Skin Care</a>