Almost all graphics software has a layering feature, the purpose is to manage objects on the drawing, making it easy to edit without mess when a drawing has many types of objects on it. . Some popular features include:
Turn On / Off Layer : turn off and open the layer
Lock / Unlock Layer : lock and unlock the layer
Frezze / Thaw Layer : freeze and melt layers
Isolate / Unisolate Layer : only show 1 selected layer, the remaining layers are turned off
Layer Color : change the layer color
Layer Linetype : change the display line type of the layer
Layer Lineweight : change the line thickness of the layer