The full, step-by-step guide lives in the repository: docs/GETTING-STARTED.md. The short version:

1. Install it. Download the installer for macOS or Windows from the Releases page, or build it from source (the guide shows how). Your system may warn that the app is from an unrecognised developer; that is about code signing, not about what the app does.
2. Choose how your data is protected. A passphrase you type each time is the stronger option. "Open automatically" is more convenient and relies on your computer's own login and disk encryption.
3. Write down the twelve words. They are the way back in if you forget your passphrase or move to a new computer. Nobody can reset them for you.
4. Pick a backup folder in Settings, so copies exist somewhere other than the machine itself.
5. Import a statement. Drop in a CSV, Excel or PDF from your bank. Coin Heaven works out the layout and shows you what it understood before it saves anything.

If you would rather look around first, Settings has a "sample household" you can load and remove again.