Add ringo and owl.js to your PATH. E.g. assume you checked out this repo into a ~/repos directory:
export PATH=$PATH:$HOME/ringojs/bin
export PATH=$PATH:$HOME/repos/owljs/bin
I'm currently working on installation via rp, the ringo package manager. For now, do this hacky measure:
cd $RINGO_HOME/packages/
ln -s ~/repos/owljs owl
ln -s ~/repos/owljs owljs