Sam's photofact Help

I downloaded my first Sam's Photofacts yesterday and need some help. To clarify my skill level I am really a Plumber who works with Pipes and ..... I know there is a way to determine if the circuit is working by measuring voltages at different points, I assume that is what the black boxes with numbers are about??? How do we do that?? also there is the Truth Chart I get what it is about but how do i do it??

Is there a how to use sams manual or am I really as dense as I feel<GRIN>

Thanks...

Sam's photofact Help