A good place to start is http://www.php.net you can get some tutorials there and go ahead and download the php manual
the symbol for or is || even just using 'or' works
eg This ...
if($item1 == '$itemx' || $item2 =='$itemy')
{
code comes here;
}
is the same as...
if($item1 == '$itemx' or $item2 =='$itemy')
{
code comes here;
}