Installing manually
The generic setup instructions boil down to

1. Installing Python 3, including pip.
2. Creating a virtual environment somewhere: python -m venv OctoPrint
3. Installing OctoPrint into that virtual environment: OctoPrint/bin/pip install OctoPrint
4. OctoPrint may then be started through ./OctoPrint/bin/octoprint serve or with an absolute path /path/to/OctoPrint/bin/octoprint serve

This starts it up manually

/path/to/OctoPrint/bin/octoprint serve