Refund is given when excess income tax is paid over actual liability. In order to know how to calculate refund, it is important that you know how to calculate income tax liability. This can be done only when you know about the following, at least:
1. Various heads under which income is taxed and tax computation
2. Exemptions/ deductions / relief / rebates/ set off
So what I suggest is that you need to read about the above sections (min) in order to understand Income tax act. Since you are an accountant, it would not be difficult for u to understand all these.