There are several programs for using git on Windows. Github for Windows and TortoiseGit are both good alternatives.
Github for Windows
TortoiseGit
File comparison tools
To merge two files with the help of a file comparison tool you can see a comprehensive list of programs on this Wikipedia site. Meld is a recommended choice.
License
When you are asked for a license when creating a new repository, choose the GPLv3 license.