The uiBuilder uses a block based system to allow you to build in a modular way. Blocks can be added from various places within the uiBuilder to allow you to build the way you want.
From the blocks panel
The blocks panel can be accessed from the left panel of the builder and clicking on the blocks tab. Blocks here can be dragged into your template to wherever you want them to go.
From the layers panel
The layers panel which is also located in the main left panel of the builder allows you to add blocks directly in the position specified.
Under any block that allows content, you will see a plus symbol, clicking this will reveal a dropdown of available blocks that can then be added by clicking them.
Within the template
You can also add blocks to blocks that allow content via right clicking them within the template. This will reveal the contextual block menu, you will see in this menu a ‘insert’ option. Clicking this will reveal a block list when blocks can be added by clicking.