ETF is a product build around an asset. The price of the ETF is supposed to mimic the price of the asset. For example, Nifty Bees is an ETF, the price of which mimics the asset - which is Nifty Spot. Goldbees is an ETF which mimics the price of Gold in spot. So an so forth.
One of the advantage of an ETF is that it can be bought in a single unit…for example you can have 1 Nifty Bees, which is as good as saying you hold 1 unit of the Nifty Index. Its convenient and hassle free.
It is the responsibility if the company running the ETF ( Goldman Sachs runs most of the ETF’s in India) to ensure that the price of the ETF exactly replicates the underlying asset. There is a metric called “Tracking Error” which helps us identify the well managed ETF from the bad ones.
So when you buy your ETF, ensure the tracking error is low!