How new add user can log in

I can help you figure this out, useralmanazal-gas.

Please have your new user check his log-in credentials. 

You may also ask if he has a User ID with the invitation that asks him to sign in. If not, he'll receive a link on the email sent to let him create a User ID so he can sign in to your QuickBooks account. 

I've attached this article for additional information: Get help if you can't sign in to your QBO account.

Once your new user is able to get into your QBO account, here's a link to get started with QuickBooks Online.

The Community is always here to help whenever you need assistance while doing tasks in QBO.