At time of purchasing gold....
You need to pay GST @3%
At time of selling of gold,
Two situation may arise:
A. Gold sold within 36 months will be treated as Short Term Capital Asset and hence STCG may arise..

B. Gold sold after 36 months.....Then LTCG will arise...You will get indexation benefit on such LTCA..

If you intend to buy gold bars out of money gifted to you on your marriage, the tax treatment for the purchase and sale of gold bars is as follows:

Purchase of Gold Bars:

There is no income tax applicable on the purchase of gold bars out of money gifted to you on your marriage.
However, ensure that the source of the money used to purchase the gold bars is from a legitimate and legal source.

Sale of Gold Bars:

If you sell the gold bars within three years of the purchase, the profit or gain arising from the sale will be considered as short-term capital gains and will be taxable as per your income tax slab rate.
If you sell the gold bars after three years of the purchase, the profit or gain arising from the sale will be considered as long-term capital gains and will be taxed at a flat rate of 20% with indexation benefit.
In case the sale consideration exceeds Rs. 20 lakhs, TDS (tax deducted at source) may apply at the rate of 1% under section 206C(1H) of the Income Tax Act, 1961. However, if you can provide your PAN and other details, it will reduce the TDS rate to 0.1%.
It is important to maintain proper records of the purchase and sale of gold bars, including the purchase invoices, sale invoices, and other related documents. This will help you calculate the capital gains accurately and file your income tax return correctly. If you are selling the gold bars through a dealer, they may also ask for the relevant documents to comply with the KYC (know your customer) and anti-money laundering norms.