Edit in JSFiddle

<div id="UserTable">
<table>
<tr>
<th>Name</th>
<th>Email</th>
<th>Password</th>
</tr>
<tr>
<td>Jack Wilshere</td>
<td>Jack@gmail.com</td>
<td>Wlshere</td>
</tr>
</table>
<input type="button" id="createUser" value="Create User" />
</div>

<div id="dialogForm" title="Create User">
<span id="warningSpan"></span><br /><br />
<form>
<label for="name">Name</label><br />
<input type="text" name="name" id="name" /><br />
<label for="email">Email</label><br />
<input type="text" name="email" id="email" /><br />
<label for="password">Password</label><br />
<input type="text" name="password" id="password" /><br />
</form>
</div>

$(function () {
        $("#dialogForm").dialog({
            autoOpen: false,
            height: 400,
            width: 350,
            modal: true,
            buttons: {
                "Create User": function () {
                    createNewUser();
                },
                Cancel: function () {
                    $(this).dialog("close");
                }
            }
        });

        $("#createUser")
			.button()
			.click(function () {
			    $("#dialogForm").dialog("open");
			});

});


function createNewUser() {
    var nameValue = $("#name").val();
    var emailValue = $("#email").val();
    var passwordValue = $("#password").val();
    $("#warningSpan").text('');
    var isValid = validateForm(nameValue, emailValue, passwordValue);
    debugger;
    if (isValid) {
        $("#UserTable tbody").append("<tr>" +
							"<td>" + nameValue + "</td>" +
							"<td>" + emailValue + "</td>" +
							"<td>" + passwordValue + "</td>" +
						"</tr>");
        $("#dialogForm").dialog("close");
        $("#name").val("");
        $("#email").val("");
        $("#password").val("");
    }
}

function validateForm(name, email, password) {

    var isValidName = true;
    var isValidEmail = true;
    var isValidPassword = true;

    if (name == '') {
        $("#warningSpan").text("name is mandatory!");
        isValidName = false;
    }
    if (email == '') {
        var warningSpan = $("#warningSpan").text();
        if (warningSpan != null) {
            $("#warningSpan").append("<br /> email is mandatory!");
        }
        else {
            $("#warningSpan").text("email is mandatory!");
        }
        isValidEmail = false;
    }
    else {
        var regex = /^([\w-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([\w-]+\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(\]?)$/;
        if (regex.test(email)) {
            isValidEmail = true;
        }
        else {
            isValidEmail = false;
            var warningSpan = $("#warningSpan").text();
            if (warningSpan != null) {
                $("#warningSpan").append("<br /> email is not in correct format!");
            }
            else {
                $("#warningSpan").text("email is not in correct format!");
            }
        }
    }
    if (password == '') {
        var warningSpan = $("#warningSpan").text();
        if (warningSpan != null) {
            $("#warningSpan").append("<br/> password is mandatory!");
        }
        else {
            $("#warningSpan").text("password is mandatory!");
        }
        isValidPassword = false;
    }
    if (isValidName && isValidEmail && isValidPassword) {
        return true;
    }
    else {
        return false;
    }
}

table td,th
{
    border:1px solid black;
    width:400px;
}
table
{
    border:1px solid black;
    border-collapse:collapse;
}