A probe is an element that simply displays the value at a given point in a circuit. It does not itself interact with other components.
In most respects, the probe component duplicates the functionality found in a Pin component configured as an output pin. The primary difference is that if the circuit is used as a subcircuit component, then an output pin will be a part of that interface, whereas a probe is not. They also are different in that the probe does have a Data Bits attribute to be configured: The bit width is inferred from whatever value it happens to see on its input. Graphically, they are similar but have slightly different borders: A pin has a thick, black border, whereas a probe has a thin, gray border.
A probe component has only one pin, which will acts as an input to the probe. The width that this pin accepts is adaptive: The probe will adapt to inputs of any width.
Poke Tool Behavior
Text Tool Behavior
Allows the label associated with the component to be edited.