i m a beginner in open source contribution,so can anyone please guide me through the procedure.
i have read the procedure given on the website and followed them but now i am stuck with the cmake part in building the project.
Therefore,
Please can u tell me about the entire step by step procedure from how to find whether a bug is active or not to downloading its corresponding repository.

You need to be a tad more specific what exact program you are contributing to, there are several dozen applications made by the KDE community.

Also each program has their dedicated mailing list and forum section, as well as IRC channel, so you really need to be more specific and subscribe to the correct lists. Once subscribed to the dedicated mailing list, introduce yourself to the team (ideally with a bit more background about your skills), they will point you in the right direction.

I was attempting to work on kdialog under bugs for beginner
So which irc channel to join

I presume that would be kde-devel, then. Please make sure to search and read all the documentation for contributors on our wikis. There are plenty of guides for beginning contributors, and since our projects are all volunteer driven, you need to rely on doing your homework first, as there will not always be somebody around immediately when you have a question.

Our policy is that a good developer is able to find its way around the internet without having to ask for elementary information. So if you have questions make sure you have done your homework and know what you are talking about.

Did you start yet? Where will you source it?

I was attempting to work on kdialog under bugs for beginner
So which irc channel to join

You can go to #kde-devel on irc.freenode.net, but don't expect hours of hand-holding. If you have specific questions, you can ask them there, but be patient