Auto Generate Password
This will remove the password field from registration forms. WordPress will automatically generate and send a random password to the user post successful submission of the form.
Send Username and Password to User Through Email
Post registration, if site admin wants to send username and password information to the user as plain text, this setting should be turned on. As a general security thumbrule, it should be avoided. Note that, this email is separate from auto-responder email sent to the user, which admin can configure.
If Auto Generate Password is enabled, then this email is always sent irrespective of the setting.
WP Registration Auto Approval
Turning this toggle button off will disable automatic activation of WP user accounts. Admin will have to manually activate each account by browsing through the submissions. Comes handy, if you want to manually approve each submission for registration.