This is one of the most interesting sections in the Graphics Editor. Click on it and you'll have a whole lot of different categories to choose from. Select one, and get access to tons of objects to add to your masterpieces.
To add the object, just click on it, and it will appear on your template.
You can move and rotate objects, resize them and move them back and forth on your picture.
You can also choose the color, opacity, contrast, saturation and brightness of your object.
To find out how you can use the hex code to change the colour, please check out this article.