How do I turn my laptop into a PA system?

by ecbrenn
(Central California)

I teach school and use a laptop and a Smartboard. I am always having to speak very loudly to be heard and when students speak, most of the time they cannot be heard. They speak softly. They are 10 and 11 years old and mostly from a culture that discourages loudness in children.

I bought a microphone, but it seems it cannot be used with the laptop and speaker set up I use to play CDs and with the Smartboard.

Can I use my laptop and speakers and mic to amplify my voice in the classroom? Is there a hack for this or downloadable software?

Is there a way to make a system with three or four mics so I can use one and place a two or three in the room where students could go to speak?