the dot means "concatenate" or "make these strings into one big string".
$sTotal = "left"."right";
now $sTotal will contain "leftright";
or:
$sLeft = "left";
$sRight = "right";
$aTotal = $sLef.$sRight;
now $sTotal will contain "leftright";
$sLeft = "left";
$sRight = "right";
$aTotal = $sLef." and ".$sRight;
now $sTotal will contain "left and right";