Take your button and observe the metal prongs on the bottom. Usually, the two pairs curve towards the inside of the button. There is one in and out on each side, and each pair with the same curve has one of each. Keep this in mind when placing it on the breadboard, shown in the following image:

 When you're placing a button on the breadboard, you'll want to make sure that the button crosses the trough in the middle of the breadboard in order to prevent a short. 

Once you've placed the button into the breadboard, make sure it's well-seated, and that none of the prongs have curled up into themselves instead of going into the breadboard socket. If one has, use needle-nose pliers to straighten it.

Now that you've got your button on the breadboard, it's time to wire it to your Pi.