You should have completed the earlier Setting up PaaS with OpenShift Origin recipe.

Make sure your cluster is up and running:

$ oc cluster status

Clone the OpenShift Git repo into the /opt/openshift/origin directory:

$ mkdir -p /opt/openshift
$ cd /opt/openshift
$ git clone https://github.com/openshift/origin.git
$ cd origin/examples/sample-app

Your current working directory should be /opt/openshift/origin/examples/sample-app inside the VM.