Add the Block Builder module to the webpage, click the Open edit mode button. This will open the widget with the selection of elements and categories. Elements are organized by categories. By selecting a category, you can see the elements included in the category. You can then drag & drop elements on the webpage.
In order to create a grid to which elements are added, select one of the offered layouts in the Layouts section and drag & drop it on the webpage.
An element added to the page can be edited by double-clicking the element, which opens the quick edit mode. Quick edit mode allows inline element text editing. By clicking Close quick edit, you can exit the inline element editing function. Images can be replaced and added by clicking Replace. In the upper left corner, there is an icon which opens the edit mode with full HTML editor, which also allows editing the HTML code. After you finish editing, click Close edit mode and then click Save. To exit the widget, click Close edit mode.