After reading all articles I got that the number inside [:] means packet counter and bytes counter.
But what I did not understand and did not find anywhere is what the number means and important. I mean when I write [0:0] ---> what I came to know is that it will accept all data coming from any network. When will I write [7752:8249066] what will happen? Please clear me this and how I will decide which number to use?
According to this other Answer
What do numbers in INPUT,FORWARD,OUTPUT chains mean in iptables config file?
The Numbers in Brackets are Statistical Values that the Command iptables-save reads from the running Firewall representing the Traffic that has been filters by the Chain.
You cannot assign them your own Values for any desired Traffic Rates or Bandwidth.
Values like
*filter
:FORWARD ACCEPT [0:0]
simply mean that this Chain never had been used. Likely because it does not have any Rule.
