clearing basics: semi-OT

[Payal Rathod <linux@rpayal.cjb.net>]

Hi,
I am trying to clear some of my basics. I am reading IP-Masquerading HOWTO. 
In it these things were mentioned,

UNIVERSE="0.0.0.0/0"
$IPTABLES -A INPUT -i lo -s $UNIVERSE -d $UNIVERSE -j ACCEPT

What exactly does 0.0.0.0/0 mean? And why should we be concerned with
it? And what is the use of rule given after it?

INTNET="192.168.1.0/24"
INTIP="192.168.1.1/24"

The first one means the entire network of 192.168.1.x? What exactly is
the second one. Does it just means 192.168.1.1 then why "/24"?
And lastly,

$IPTABLES -N drop-and-log-it
$IPTABLES -A drop-and-log-it -j DROP

Why was this rule made? And why was it "dropped"? What is the logic
behind this? Shouldn't it be,
$IPTABLES -P drop-and-log-it DROP


Thanks a lot for the patience and bye.
With warm regards,
-Payal

p.s please make a cc to me too.

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