Description / Line Console 0 / Logging Synchronous

I got an email today from one of my friend from india (we came to know about each other on cisco community on orkut :)

Mr. XYZ

"hi sohail,
how are u ?. I am fine and hope same for u. I have some problem in CCNA. so i am writing this mail..
what is the use of command
line console 0 and why we always should use 0 with this . if u will use this command in a router with a question mark
such as
Router(config) # line console ?
<0-4> first line number
Now this time it has five choices,we can use any number but the output is not coming as we want, I referred CCNA books but i could not get the answer. if it is necessary to use always 0 then why it gives five choices. I am not able to understand.

my second problem is
when i am typing some commands in router configuration mode I am getting some unwanted messages. how to remove these messages . mainly it is coming when we are typing in some commands. I got a answer that was use logging synchronous command, but i don't know how to use this command. and what will be the effect of that command we will get.

my third problem is
how to use description command and why ? "

Reply:

Ans # 1: Man u r getting it wrong, in router the console command is always <0-0>, this is just usaed to enable the console password and 0 menas the zero level and it is always 0 see attachement with mail, i have attached the router snap short for u, while configuring the passowrd so when u enter there an option is wheather to ask for it r not i mean
no logging OR logging

Ans # 2: We can log the messages to the console without interferring with your work in the console in Cisco IOS by logging synchronous.In Cisco IOS, logging synchronous can allow you to work along with the logs still logging to the console but without disturbing your work.
To do this
Consoole Port:
Router(config)# line con 0
Router(config-line)# logging synchronous
AUX port:
Router(config)# line aux 0
Router(config-line)# logging synchronous
for telent/ssh:
Router(config)# line vty 0 4
Router(config-line)# logging synchronous
If ur switch or router has many vty session
Router(config)# line vty 5 15
Router(config-line)# logging synchronous
or if you want to off then use NO with the commands.

Ans # 3:First why we use description, so description is used to remember the things in the future suppose in very large networks it is not possible all the interface and stuff that belong to whom, so better is to give some description to the interface etc to remember that.

How to use:

# interface serial 0
# description T1 Line to Head Office - 256 Kb/s