Should get benefit for contributing in HSA account, however when I enter HSA amount in "W-Box12". It increases the tax amount. Cant understand why ?

Just keep going and ignore the refund meter. When you enter an HSA contribution through box 12, TurboTax assumes that it is taxable until you get to the following questions that ask whether you had qualifying health insurance for the year. Once you indicate that you did have a qualifying health plan that makes you eligible for HSA contributions, it will be removed from your taxable income again.  I believe there is a question about health insurance as part of the W-2 interview after you enter an HSA amount, or you can access the health insurance questions in the HSA interview on the deductions and credits page.