wiring w/ dual speaker terminals

all these wiring diagrams show amps with only one speaker terminal.. what is the difference when there is 2 speaker terminals on a mono amp? can i only use on set of terminals for 2 or more subs? or would that damage my amp? Id appreciate any help.

Yes, you can use just one set of the terminals.  The pairs are internally connected and so are in parallel.  This shows the internal connections:

You actually have to be very aware of what you're doing if you do use both sets of terminals.  Not knowing that paralleling will halve the impedance can cause problems.