How to add spacing between columns?

I have two columns:

<div class="col-md-6"></div>
<div class="col-md-6"></div>

How can I add a space between them?

The output would simply be two columns right next to each other taking up the whole width of the page. Say the width was set to 1000px then each div would be 500px wide.

If I wanted a 100px space between the two how could I achieve this automatically with Bootstrap: the divs sizes would become 450px each to compensate for the spacing.

I was facing the same issue; and the following worked well for me.

<div class="row">
  <div class="col-md-6">
     <div class="col-md-12">
        Some Content.. 
     </div>
  </div>
  <div class="col-md-6">
     <div class="col-md-12">
        Some Second Content.. 
     </div>
  </div>
</div>

This will automatically render some space between the 2 divs.

You can achieve spacing between columns using the col-md-offset-* classes, documented here. The spacing is consistent so that all of your columns line up correctly. To get even spacing and column size I would do the following:

<div class="row">
  <div class="col-md-5"></div>
  <div class="col-md-5 col-md-offset-2"></div>
</div>

In Bootstrap 4 use: offset-2 or offset-md-2

I know I'm late to the party, but you could try spacing the boxes with padding.

<div class="col-md-6 box">
        <div class="inner">Hello</div>
</div>
<div class="col-md-6 box">
        <div class="inner">Hello</div>
</div>

CSS:

.box {
    padding: 0 5px 0 5px;
}
.box .inner {
    background-color: #fff;
}

Have a go at it