OpenEmbedded-Core is a layer containing the core metadata for current versions of OpenEmbedded. It is distro-less (can build a functional image with DISTRO = "nodistro") and contains only emulated machine support.
For information about OpenEmbedded, see the OpenEmbedded website: https://www.openembedded.org/
The Yocto Project has extensive documentation about OE including a reference manual which can be found at: https://docs.yoctoproject.org/
Please refer to https://www.openembedded.org/wiki/How_to_submit_a_patch_to_OpenEmbedded for guidelines on how to submit patches.