You should never be storing your coins on a online wallet / exchange.
There is no guarantee coinbase is going to pay you those BTG out.
Coinbase has the control over your private keys (the real bitcoins). You only have an account on their website which gives you "the right" to send coins.
In case of a fork coinbase is in charge of the BTG coins. They may give them to you.. or they dont.
I would recommend to download a wallet for your PC (you can download a light weight wallet e.g. electrum)
Today I downloaded electrum wallet,but i am confused there is a address tab and i can see there are many address listed there,Those are my address?or this wallet changes address every time i want to receive bitcoins.I have made 2fa verification on there does that cost me extra money if so how much it will be,
I am new could anyone help?
Yes, those are all your addresses.
Electrum generates a new address for every transaction (for privacy reasons).
Those are all addresses which you are in control of.