Clients have their own Client Portal, where they can see their Shoots and related items such as Invoices, Contracts, Galleries, Design Proofs, etc. Clients can log in to their portal by visiting your main portal.
You can view/edit your portal URL by brand in Settings > Branding > Brands. You can also send the link to your clients by using the "Client Portal" variable in an email.
Setting the client's username
When you first create a client, their username is set to be their first and last name. You can manually override it when editing the contact. select the three dots on the right side and click "Edit".
Setting the client's password
The password for the client is not set initially, but you can send a link for them to create a password once the shoot is booked. Clients can reset their password by clicking the "Forgot Password" button on the login page.
If you want to set the password for the client yourself, you can edit the contact, select the three dots on the right side, click the "Set/Reset Password" button, and set the password.
Note that you won't be able to see the password again for security reasons.