Show and hide elements in JQuery
First, you have multiple functions with the same name.  That's not valid.

Assuming these sections are divs, to hide all of them except one, take a look at the not function:

function reveal1() { 
    $("div").not("#section1").hide("slow");
    $("#section1").show();
}


Or more generically:

function revealThisElement(elementId) { 
    $("div").not("#" + elementId).hide("slow");
    $("#" + elementId).show();
}

$(".icn_1").click(function() { revealThisElement("section1"); });
$(".icn_2").click(function() { revealThisElement("section2"); });
$(".icn_3").click(function() { revealThisElement("section3"); });


Or better yet, why not try something like this:

$(".revealable").click(function() { 
   revealMe(this); 
});

function revealMe(element) { 
    $("div.revealable").not("#" + element.id).hide("slow");
    $(element).show();
}