Select the Emoji from the list (In the top select the categories. With Up and Down arrows search for the desired emoji) and Click it(or tap in your phone or tablet).
The items always appears at the top left corner. Move the emoji where you want.
Change the background color: Click (or tap) the "Background" tab. Choose the color clicking in the selector (or write the RGB in Hexa).
Add shapes: In "Shapes" tab first, select the color, then click on the shape.
Add bubbles: In "Bubbles" tab first, select the color, then select one Bubble
Add text: In "Text" tab write the text, then select the color and finally click the "Create" button.
Toolbar buttons description (except the download button, the others only apply to the selected object):