Install as if a normal FluxBB install from the feature-textpattern-forum branch.
After which you would follow the standard FluxBB installation steps.
Development happens in the feature-textpattern-forum branch:
$ git clone --branch feature-textpattern-forum git@github.com:textpattern/fluxbb.gitTo create a patch:
$ git diff master feature-textpattern-forum > feature-textpattern-forum.patch