Can Wcart email a customer their login details when I create their account?

Yes. On Customers → Manage Customers → Add Customer (the Add User page):

1. Fill in the required fields: Name, Phone Number with Country Code, Email and Password.
2. Under the password, tick confirmation to send a mail.
3. Click Add User.

Wcart then emails the customer their login email and the password you typed. If the box is not ticked, nothing is sent and you need to pass the password on yourself. The email counts towards your store's monthly email allowance.