Have you done a Google search?

If you want information  from a list, please provide much more information.
This is a very wide subject. What specifically don't you know about it?

Actually I want to start from the basic
theory of budgeting and forecasting and then if I can find some Q&A
which could help me assisting our Managers while budgeting for our
organization. I tried to search in Google but couldnt find the
relevent information. Though I have studied this topic but cant
remember anything now which i could apply at work place.

It sounds as though you are trying to study the topic of budgeting and
forecasting, rather than wanting to ask a specific Excel question.

I think you need to work out what you want to accomplish (i.e. talk to the
managers on how they do their budgeting) and then possibly look at using
Excel to assist with the task. Don't start with a solution and go looking
for a problem.

In summary ... talk to your managers, they already know how to budget and
forecast.