The patches are for memory safety flaws, some that expose users to remote code execution attacks. While other vulnerabilities allow bad actors to track devices, terminate WiFi access and access sensitive data in the iCloud Photo Library.
You can download iOS or iPadOS 15.6 by going to Settings > General > Software Update.
Along with patching vulnerabilities, the new iOS 15.6 fixes flaws in the system like one that incorrectly shows users their storage was full or how a tab in Safari reverts to a previous page on its own.
