Where can I download the Windows installer for Drush? I cannot find the link where to download Drush windows installer.
Can anyone tell me if there is or how to do?

I am using Drupal 8.1 and Windows 7.
You need to install it using composer as specified here:

https://github.com/drush-ops/drush/blob/master/docs/install.md

After installation, make sure to run and use the drush command inside Git's shell only (the shell environment bundled with Git for Windows)