Welcome to the page builder documentation, I will explain how the page builder works.
When you are editing your page you should see the page builder meta box on the bottom of your page.
Something like this
Click on one of the modules button to add the module to the page builder, I will add the blog module.
You can modify the module size by clicking on the arrows, the left one will reduce the module size, the right will increase it.
I increased the blog module size from 1/4 to 2/3
You can open the module settings window by cliking on the wrench icon
You can remove the module by cliking on the delete icon
You can drag and drop the module to change his position, on the next picture I am moving on of the icon box module
When you click on the wrench icon the module settings window will appear, below you can see the blog module settings
On most of the modules you can set a heading and set the top and bottom margin, click on save when you finished editing the settings and do not forget to publish your page