Is there any API for programmers?

I'm a developer and I'm customizing a theme for a site, this site uses Membership plugin so I need to get current logged in info plan details as for example plan name, expire date and every around the plan, I'm search for Membership API but doesn't found nothing, just this manual (https://premium.wpmudev.org/wp-content/uploads/2010/05/Membership-Manual3450.pdf) which is for frontend and also is outdated, can you give me some advice around this?