If you have filed a tax return for 2018 or 2019 return and have provided your bank information for direct debit or direct deposit, then the IRS already has your bank information. If you did not provide your bank information on either return, then you can use the IRS portal which be ready in the coming weeks to provide your bank information so that the IRS can direct deposit your stimulus payment.
If you are not required to file a tax return for 2018 and 2019, then you can register for the stimulus payment on this TurboTax web portal.