1. Create Row

                 <div class="row"> </div>
                 

3. Create coloumn

                 <div class="row">
                    <div class="col-8">col-8</div>
                    <div class="col-4">col-4</div>
                   
                </div>

                

3. divide col 8

                <div class="row">
                      <div class="col-6">.col-6</div>
                      <div class="col-6">.col-6</div>   
                </div>
            

Complete code

            <div class="row">
                  <div class="col-8">
                        .col-8
                        <div class="row">
                                <div class="col-6">.col-6</div>
                                <div class="col-6">.col-6</div>
                        </div>
                  </div>
                  <div class="col-4">.col-4</div>
            </div>