In order to configure gmail for Drupal 8 on Windows the best way is to install the SMTP Authentication Module from here (I have installed by downloading the zip of the latest dev version). Then you can enable and go to its configuration to set-up the following in case you have a gmail account.
- Turn module on
- SMTP server: smtp.gmail.com / smtp.uth.gr (my university)
- Leave SMTP backup server empty
- SMTP port: 465 / 587 (my university)
- Use encrypted protocol: Use SSL / TLS (my university)
- Username and Password as appropriate
- e-mail from address complete with your gmail e-mail
- e-mail from name fill in the desired name
- Check Allow to send html formatted emails
- Leave the rest as default
You can ask last for a test email to be sent, this should be working also.