Layer

Organizing objects in a drawing by function or purpose
Layer can reduce the visual complexity of a drawing and improve display performance by hiding information that you don't need to see at the moment

Home tab > Layers panel > Layer Properties

Layer Visibility

ON / OFF 

OFF: Objects on the layer invisible but still regenerate
        Objects on the off layer are not plotted

Thaw / Freeze 

Frozen: Objects on the layer invisible and not regenerate
            Objects on the frozen layer are not plotted

Locking Layer 

Objects on the layer are visible but appear faded, and cannot be edit.
Objects on the locked layer are plotted

A lock icon appear to indicate the object on the locked layer

Using Layer

Make Object's Layer Current

Sets the current layer to that of a selected object
Change the current layer by selecting an object

Layer Transparency

Apply transparency on layer make objects on the layer appear lighter in color

The higher the value, the more transparent the object appear.

Isolating Layer

All layers except the layers of the selected objects are either turned off, frozen or locked, depending on the current setting.
The layers that remain visible and unlovked are isolated