These symbols are often use to represent electrical node name.
These symbols represent electrical objects that do not have corresponding physical components.
Classic examples are ground and voltage symbols. They have:
•Graphics that help to illustrate their functionality.
•A single electrical symbol terminal that you can connect a schematic wire to.The all the symbols below, the symbol terminal are invisible to electronic engineers instinctively know where they are.
Ground Symbols
Voltage Symbols
When you move the mouse cursor over a symbol terminal, the cursor turns green showing you that a connection can be made to/from this point.
Green Cursor Over Connection Point
 Start Point OK |
 End Point OK |