If you want images in your columns you will need to click between the

<div class="column"></div> tags

Then click on Add Media and upload the image to your media library. Stay in text editor to do this, as the code will automatically be generated for you.

Once you have completed inserting your images in each tag you will see this, although obviously the code will be different to that shown in the example below:

Now go to Preview and you should see this, although your images will be different:

OK so far? So let's insert some text.