Membership Pro is a Joomla extension, so you need to have a website built on Joomla CMS to use the extension. Please look at https://www.joomla.org/about-joomla/technical-requirements.html to see technical requirement for your server. Latest version of Membership Pro only works with works with Joomla 3.9.0+. If you are using older Joomla version, submit a support ticket asking us sending old version of the extension which works with the old version of Joomla which you are using.
Membership Pro is also require PHP 7.4.0+ to work. If your site is running on older version of PHP, please contact your hosting provider, ask them to change settings for your hosting account to use PHP 7.4.0+.