Make sure you are using Windows 7 or above.
1. Download Book Keeper from website: http://bookkeeperapp.net/
or you can directly download from this link: http://bit.ly/bk-windows-direct
2. Go to Download folder, where it is downloaded, and double click on it to install it.
Here's video tutorial on how to install: https://www.youtube.com/watch?v=aCPjnGo7c9s
If it asks for .NET framework, please refer to this link: https://bookkeeperapp.zendesk.com/hc/en-us/articles/360002733514-It-is-asking-for-NET-framework-while-installing