Beta testers who have signed up for Apple's beta testing program will receive the iOS 10.3.2 beta update over-the-air after installing the proper certificate on their iOS device.
Those who want to be a part of Apple's beta testing program can sign up to participate through the beta testing website, which gives users access to both iOS and macOS Sierra betas. Betas are not stable and include many bugs, so they should be installed on a secondary device.
Apple has said that the update fixes SiriKit car commands, which should now be working as expected. Beyond that, we don't yet know what features or improvements are coming in iOS 10.3.2, as Apple doesn't offer detailed release notes and nothing notable has been discovered in the betas we've received so far.
As a minor 10.x.x update, iOS 10.3.2 likely focuses on bug fixes, performance improvements, and security enhancements rather than outward-facing features.