It is a library, as already linked in the other comment: https://github.com/landlock-lsm/go-landlock
The landrun tool is built on the same library. We also provide an official library for Rust, and obviously you can do it from C as well.
I also collected some libraries for other languages at https://wiki.gnoack.org/SoftwareUsingLandlock (but I can not vouch for their quality in detail)