Which way will I place a momentary Tactile switch in a solderless breadboard
Perhaps this drawing will help.


As you can see on the right hand part of the part of the diagram pins 1 and 2 are connected together. Pins 3 and 4 are connected together and the switch action is between these pairs of pins. 

Using a multimeter set to low ohms (resistance) you should find that the two sets of pins that are short circuit. These correspond to pins (1,2) and (3,4) in the diagram. 

To get a switch action you need to connect one side of your circuit to pins 1,2 and the other side to pins 3,4. Of course you do not have to connect both pins on each side of the switch. It will work by connecting 1 and 3 or 2 and 3 etc.

a data sheet can be found here http://www.omron.com/ecb/products/pdf/en-b3s.pdf