How do I reset a user’s password or email them when I create an account?
If you are an administrator or your account has “administrate users” privileges, then there is a checkbox on the user’s edit page in the control panel that says “Require Password Reset on Next Login” which, if checked, will force the users to reset their password the next time they attempt to login.

When creating a new account, if you leave the “Require Email Verification” checkbox checked, the user will get an email asking them to confirm their email address and set a new password on their account when the click the link in the email.

Note that the password reset and account verification process requires email to be configured and working properly under Settings->Email in the control panel.