The Layers panel (Window > Layers) is used to organise, list, and modify the objects included inside a document. By default, each new document includes a single layer, under which each item you create is listed. However, you may add additional layers and rearrange things to suit your own requirements.
Step 1:
Click the name of the layer above (or inside) which you wish to create the new layer in the Layers panel.
Step 2:
To create a new layer above the currently chosen layer, in the Layers panel, click the Create New Layer button.
Step 3:
To create a new sublayer inside the currently chosen layer, in the Layers panel, click the Create New Sublayer button.
Step 4:
To configure settings for a new layer, choose New Layer or New Sublayer from the Layers panel menu.
Step 5:
The Draw Behind mode generates an active new layer behind the current layer automatically.
Step 6:
If no artwork is chosen, artwork is drawn behind all artwork on a selected layer in draw behind mode.
I hope that this tutorial was easy to understand, make sure to watch the video for further clarification.