Note: The Password field being enabled is a result of the "Administrator can set user passwords" option under your User Sign-In Policies.
You can send any new User two emails via the [Send E-mail] button. The first email will contain their User Name, Server Name, and Port Number - the information required to initially log in to SI 2018. There is also a link to download the latest SI 2018 Client so they can install it on their machine if this has not already been done. The second email contain their password.