Is creating channels necessary. What is it important for. Till now i have not yet created. I just run adds on thre four sites. How do i create channels and how do i manage them. What is the channel no? Do i need to specify the channel with a particular number or google gives you that number after you create channel.

Creating a channel is to show you with more detail what ads (in what places) get the best exposure and clicks

You set them up before the last step of the adsense setup and you specify your own name and its included in the code that google gives you for copy and paste

For example if you have in your example.com site one banner at the top and one at the bottom of each page your can specify the channels respectivelly example_top_banner and example_bottom_banner and then your can see which place is more beneficial to you

there is more to channels then that but that is a start

thank for hat but on mor thing i noticed is that last time i tried naming a channel with a site name but it allowed me only specific number of characters so i did not enter it and directly ran the adds.
Secondly for add rev sharing forums hey *** for the chanel id and pub.
If i nam the chanel as abc.com in adsense account so i need to enter that in the channel id field?
Presently i am running adds without any channels on two forums. But hardly earn any thing there.

well if adsense does not allow you to put all the characters make up shorter nick names for those ... you don't have a choice .... for example if your website is webmaster-talk.com enter wmt for a channel

yes on the forum sharing adsense money you need to put that channel code on the specified box ... you are going to get it somewhere in the copy and paste code ...