1- Once I sell bitcoin , will the money goes directly to my bank account that is link to the account ?
2- If I have bitcoin in my wallet how can I withdraw it if I need to ?
We have an article which details how to sell Bitcoin. You can sell Bitcoins on exchanges when you sold your coins, the USD amount appears on the account you have on the exchange. Then you can withdraw that money to your bank account. There are different types of wallets, an exchange stores your coins in a hot wallet, while there are also offline cold wallets, which are safer. If you store your Bitcoins in a cold wallet you have to transfer these first to an exchange to be able to sell them.