Download the latest version of the Members App checking that the minimum version of Perch is the same or less than the version of Perch that you are running.

Unzip the download where you will find two folders.

Copy the perch_members folder into perch/addons/apps/

Add perch_members to your apps.php file.

When you next log into the Perch admin the Members install script will run behind the scenes to create the necessary tables. A new members navigation item will appear in the administration menu.