When your images, texts and shapes overlap on your design, some elements will be on top of each other. To change that, you have an option called 'positioning' that will allow you to bring an element forward or backward.
This option is very useful when you are creating composite images with more than one product or doing a moodboard.
You can use the positioning button for images, text, and shades.
Bring forwards: moves a selected element one layer up within your design.
Send backwards: moves a selected element one layer down on the canvas.
You can click as many times as there are layers to bring the element forward or backward.
Here is an example: