You can get started by reading the documentation on Read The Docs. (It's quite short, I promise.)
You can also get help on #virtualfish on OFTC, the same network as the Fish IRC channel.
A quickstart, for the impatient
pip install virtualfish
~/.config/fish/config.fish, adding a line that reads
eval (python -m virtualfish)
- Add virtualfish to your prompt
vf new myvirtualenv; which python
See the docs to find out more about virtualenvwrapper emulation, auto-activation and other plugins, extending virtualfish with events, and more.