Branches on git.centos.org
The convention on git.centos.org is for packages to have a branch per major CentOS version, so you get c7, c8-beta, c8, etc. Packages in Stream 8 have a c8s branch, and that's the one you want in the vast majority of cases.
Packages in the Hyperscale SIG can have two branches: c8s-sig-hyperscale (for packages branched in the main repository) or c8s-sig-hyperscale-experimental (for packages branched in the experimental repository). In general, a SIG will have push access to all branches named c8s-sig-<signame>*.
Packages shipped as part of module streams can have additional branches, usually named <dist>-stream-<modulestream>. For example, the softhsm package has a c8s-stream-DL1 branch, signifying it is shipped as part of the DL1 module stream (of the idm module, in this case). On a running system, dnf module provides softhsm would also point out the origin of this package.