I don't have direct experience with either git or with HeeksCAD, but it does not look like there is any easy answer to your question.
From looking at the git repository to which you linked, I did not find any Windows executable there. So, I believe that in order to get a Windows version of the software, you would have to either:
- download the HeeksCAD source files from the github repository (that you linked to), get a suitable Windows compiler, and build a Windows executable from the program source (difficult to do if you are not an experienced programmer), or
- find someone else who has already built a Windows executable version, download that version and install it (but beware of possible trojan horses or viruses if you download from an untrusted source), or
- it appears that there may be a version written in Python, and if that is correct, then download that version of the software, and download a version of Python for Windows from somewhere else, and then try running the Python version, or
- give up on Windows and consider installing Ubuntu (Linux) and then download and build that version of HeeksCAD (still difficult to do, but probably less difficult than building it for Windows)
Of course it is possible that I have overlooked another option...