You can automatically create random/secure passwords for your members database and then email all the members their password and login details.
The "Create passwords" screen shows all the members who have an email address but do NOT have a password.
Clicking the [Create passwords] will simply create and save passwords for all the members listed.
Clicking the [Create and email passwords] button will create the passwords AND email the members a message containing their email and the website login details. The layout/template for the email is set by the "Auto generated password message" General setting.