To create custom elements you need to use the left side toolbar where you can find 5 types of tools.
Is a tool for manipulating with the elements by dragging, selecting and moving them.
A container that allows you to create more complex structures by nesting one element into another or combining elements.
while selecting this tool a default text is inserted that you can customize later. Text properties can be found in the right sidebar.
You can insert any type of images like png, jpg, svg using this tool.
The tool hand is used to move the page on the canvas area.