Can you explain what happens during the execution of 'git merge' and how it combines branches in a repository?

The git merge command combines changes from one branch into another. When executing git merge <branch>, Git attempts to merge the history of the current branch with the specified branch.

The process occurs as follows:

1. Git finds the common ancestor (common commit) of both branches.
2. It compares the changes made in each branch since the common ancestor.
3. It applies the changes from the target branch to the current branch.

If there are no conflicts, Git automatically creates a new merge commit that combines both histories. If there are conflicts (the same lines changed in both branches), Git will stop and ask for manual conflict resolution.

Thus, git merge allows for the integration of parallel development branches, preserving the change history and ensuring code consistency.