In the top right of the editor you will find the bar about layers. If it is not there click on the little tab marked layers to open it.
This shows that we have two layers in our project. The top layer is called "Layer Shadow" and under that is "Layer Main".
Notice next to each layer there is a tick box and a padlock. The tick box shows if the layer is visible in the editor while the padlock stops us from altering the contents of the layer. Above the list there are a few more icons - a plus, eye, padlock, pen, rubbish bin, and up/down arrows. If you hover your mouse over these then a small description will pop up about their use.
For more information on the layer bar right click somewhere on it and from the pop up select "Help".