node in selenium grid code example

Example 1: what is nodes and hubs in selenium grid

-we run this jar from 2 roles: hub and node
-hub receives commands Webdriver object of the client
-then hub is looking for available nodes 
 for execution.
-nodes are executing tests

Example 2: how selenium grid looks like

-it's a java program looks like jar file
-we run this jar from 2 roles: hub and node
-hub receives commands Webdriver object of the client
-then hub is looking for available nodes 
 for execution.
-nodes are executing tests