The Getting Started page says:

Eventually you will want to push the local repo to a remote.

yadm remote add origin <url>
yadm push -u origin master

It wasn't clear to me whether to expect the yadm wrapper to be smart enough to exclude the internal repo path from <url> or not. It turns out it is not. Perhaps it would be clearer to use <user@host:.yadm/repo.git> rather than the ambiguous <url>.

Even after doing that, it turned out that the yadm push command fails since it is rejected.

I should say first that since the text under discussion belongs to the "If you don’t currently have a repository" section, I assumed it to be reasonable to simply initialize the machine I was pushing to with yadm init (although the docs don't specify to do this, in seems necessary since yadm appears to set permissions etc. and so a clone from the local machine to the remote without an init on the remote first wouldn't do the right thing).

With that done, the push was rejected. I though maybe running yadm config receive.denyCurrentBranch warn on the remote machine would work to fix it, but that appears to be silently dropped. Instead I had to run git directly via (cd .yadm/repo.git && git config receive.denyCurrentBranch warn). That done, pushing from the local machine then worked.