I don't know what you mean by "How is gold bought in the bank" I think banks do not have precious metals like gold you can buy gold in any jewelry shop without approval from banks.

The good thing about investing in Gold the price is pretty stable and you can hold it for a long-term investment compared to investing your money in the banks with only a small P.A interest.
However, both of them are good investments because both of them will give you profit but Gold always depends on the market value it may drop or increase in value compared to banks where you can surely make a profit from the interest.