Documentation
Both the code and documentation for Gasoline are hosted on github. To get started, here are a few important links.
Building Gasoline
How to fetch the code for gasoline and compile it to run on your system.
Running Gasoline
How to run a simulation using gasoline.
Troubleshooting
What to do if the code crashes.
Getting Help
Sometimes the documentation isn't enough to solve your problem. If you are still running into trouble, feel free to send an email to the gasoline users mailing list. If you are interested in participating more closely, the N-Body Shop Slack channel is where most of the core developers hang out.