SOURCE

$(document).ready(function(){
  $("#btn1").click(function(){
    $("#test1").text("Pen!");
  });
  $("#btn2").click(function(){
    $("#test2").html("<b>Apple!</b>");
  });
  $("#btn3").click(function(){
    $("#test3").val("嗯~Applepen");
  });
});

<script src="http://cdn.static.runoob.com/libs/jquery/1.10.2/jquery.min.js">
</script>
<p id="test1">I have a pen。</p>
<p id="test2">I have a apple。</p>
<p>输入框: <input type="text" id="test3" value="菜鸟教程"></p>
<button id="btn1">设置文本</button>
<button id="btn2">设置 HTML</button>
<button id="btn3">设置值</button>