They are 2 lead
All you need is a square wave, equal to the frequency you want the piezo to buzz at.
The previous circuit I posted, with the two BJTs will do that, but it isn't the easiest way. Here's another method using the 74HC14. It's possible to use only one or two Schmitt trigger elements, but they're six in the IC and it's more stable with four: one as the actual oscillator and another three to buffer the signal to drive the piezo. If you need to use a higher voltage, than 6V, then use the same circuit, but with the CD40106, which will work up to 18V.

If you're using a microcontroller, you can just program it to output a squarewave and attach the piezo directly to the output pin. As mentioned above, using two pins, with the opposite polarities and connecting the piezo between them, will make it louder.