in front
of the vector layer or layer group name.The Layers palette displays its components like the “tree” of folders and directories in Windows Explorer. Items that have sub-components have a minus sign in front of them when expanded or a plus sign when contracted.
Expand a vector layer or layer group to see the names of its sub-components. Contract a vector layer or layer group to make the Layers palette easier to navigate.
To expand a layer or layer group:
On the Layers palette, click the plus sign in front
of the vector layer or layer group name.
To contract a layer or layer group:
On the Layers palette, click the minus sign 
in front
of the vector layer or layer group name.