column inside column in bootstrap code example

Example 1: bootstrap grid 2 rows

<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css" rel="stylesheet"/>


<div class="row">
    <div class="col-md-4">
        <div class="well">1
            <br/>
            <br/>
            <br/>
            <br/>
            <br/>
        </div>
    </div>
    <div class="col-md-8">
        <div class="row">
            <div class="col-md-6">
                <div class="well">2</div>
            </div>
            <div class="col-md-6">
                <div class="well">3</div>
            </div>
        </div>
        <div class="row">
            <div class="col-md-6">
                <div class="well">4</div>
            </div>
            <div class="col-md-6">
                <div class="well">5</div>
            </div>
        </div>
    </div>
</div>
<div class="row">
    <div class="col-md-4">
        <div class="well">6</div>
    </div>
    <div class="col-md-4">
        <div class="well">7</div>
    </div>
    <div class="col-md-4">
        <div class="well">8</div>
    </div>
</div>

Example 2: row class in bootstrap

/*
In Bootstrap, the "row" class is used mainly to hold columns in it.
Bootstrap divides each row into a grid of 12 virtual columns. 
In the following example, the col-md-6 div will have the width of 6/12 of the "row"s div, meaning 50%. 
The col-md-4 will hold 33.3%, and the col-md-2 will hold the remaining 16.66%.
*/

<div class="row">
    <div class="col-md-6"></div>
    <div class="col-md-4"></div>
    <div class="col-md-2"></div>
</div>