Single Pole:
This is the basic ON and OFF switch consisting of one input contact and one output contact. It switches a single circuit and it can either make (ON) or break (OFF) the load. The contacts of SPST can be either normally open or normally closed configurations.
Dual Pole:
This is a dual ON/OFF switch consisting of two ON positions. It has six terminals, two are input contacts and remaining four are the output contacts. It behaves like a two separate SPDT configuration, operating at the same time.
Two input contacts are connected to the one set of output contacts in one position and in another position, input contacts are connected to the other set of output contacts.