This fiddle has both each and direct json. http://jsfiddle.net/streethawk707/a9ssja22/.
Below are the two ways of iterating over array. One is with direct json passing and another is naming the json array while passing to content holder.
Eg1: The below example is directly calling json key (data) inside small_data variable.
In html use the below code:
<div id="small-content-placeholder"></div>
The below can be placed in header or body of html:
<script id="small-template" type="text/x-handlebars-template">
    <table>
        <thead>
            <th>Username</th>
            <th>email</th>
        </thead>
        <tbody>
            {{#data}}
                <tr>
                    <td>{{username}}
                    </td>
                    <td>{{email}}</td>
                </tr>
            {{/data}}
        </tbody>
    </table>
</script>
The below one is on document ready:
var small_source   = $("#small-template").html();
var small_template = Handlebars.compile(small_source);
The below is the json:
var small_data = {
            data: [
                {username: "alan1", firstName: "Alan", lastName: "Johnson", email: "alan1@test.com" },
                {username: "alan2", firstName: "Alan", lastName: "Johnson", email: "alan2@test.com" }
            ]
        };
Finally attach the json to content holder:
$("#small-content-placeholder").html(small_template(small_data));
Eg2: Iteration using each.
Consider the below json.
var big_data = [
            {
                name: "users1",
                details: [
                    {username: "alan1", firstName: "Alan", lastName: "Johnson", email: "alan@test.com" },
                    {username: "allison1", firstName: "Allison", lastName: "House", email: "allison@test.com" },
                    {username: "ryan1", firstName: "Ryan", lastName: "Carson", email: "ryan@test.com" }
                  ]
            },
            {
                name: "users2",
                details: [
                    {username: "alan2", firstName: "Alan", lastName: "Johnson", email: "alan@test.com" },
                    {username: "allison2", firstName: "Allison", lastName: "House", email: "allison@test.com" },
                    {username: "ryan2", firstName: "Ryan", lastName: "Carson", email: "ryan@test.com" }
                  ]
            }
      ];
While passing the json to content holder just name it in this way:
$("#big-content-placeholder").html(big_template({big_data:big_data}));
And the template looks like :
<script id="big-template" type="text/x-handlebars-template">
    <table>
        <thead>
            <th>Username</th>
            <th>email</th>
        </thead>
        <tbody>
            {{#each big_data}}
                <tr>
                    <td>{{name}}
                            <ul>
                                {{#details}}
                                    <li>{{username}}</li>
                                    <li>{{email}}</li>
                                {{/details}}
                            </ul>
                    </td>
                    <td>{{email}}</td>
                </tr>
            {{/each}}
        </tbody>
    </table>
</script>