It's easy to imagine a project folder with several files in it. Now imagine that you did work in the folder on two different days and saved it in two different Git branches. Or imagine a team, where you started the folder, copied it to two teamates, and they helped you improve it.
In any case, you will have the following: an older folder, that is considered the ancestor, and two newer folders. All three need to be recombined. In Beyond Compare this is called a Folder Merge session. If you want to download the files used in this example, rightclick and SaveAs this link:
Here are the 26 empty files you have set up in a project folder:
Here are the modifications your teammates made:
The easiest way to get your three folders into the above view is to drag them with the mouse. But you could also load them by browsing from the three manilla-folder icons. Or, in github, this view can open up from a
git mergetool request at the command line.
At this point, assuming every teammate has been good about saving their work, you have three different versions of the project. In the middle, is your version, the ancestor, where every file size is zero bytes. On the left and right, open your teamates folders. The file sizes show which ones have been modified. Here are the meanings of some of the symbols in this view:
As soon as you press the grey "Merge!" key at the top, Beyond Compare will irreversibly (there is no undo!) combine your files. But how can we know what is about to happen? Check out the margin of your viewer:
I encourage you to download and make your mistakes on the downloadable sample data above. After you unzip and play with that sample folder, go to the Scooter Software site. There is a good description of FolderMerge on page 30 of their official Beyond Compare documentation.