I'm having trouble understanding SPST terminology
Think of "Poles" as a piece of wire you want to connect somewhere.
And "Throws" as places where you can connect that wire to.

N Poles = N wires

M Throws = M places where you can connect each of the N wires to.

SPST

(Note that on a SPST there isn't necessarily a side which is the Pole or the Throw.)

The following might help you understand the terminology better:


To add a "Throw" you just add an extra connection on the right side. (therefore one pin at least, becoming SPDT)
To add a "Pole" you duplicate the entire thing, therefore at least 2 pins, becoming DPST.




SPDT

Following is a SPDT. Which means you have a piece of wire you can connect to two places. 


To add a "Throw", you just need to add a new place to connect it to (one more pin on the right side, having a SP3T).
To add a "Pole", you would have to add a piece of wire and two places to connect it to, therefore at least 3 pins and duplicating the entire thing. (Assuming you are maintaining it as Double Throw)




Images are from Sparkfuns explanation.