You get CONFLICT (add/add): Merge conflict in … conflicts because the files are in fact not the same. You can see the difference using the diff command, for example:
git diff branch1 branch2 -- path/to/file
where branch1 and branch2 are the names of the branches you want to compare.
Or, an easier way to see the difference, right after the failed git merge when you are in the conflicted state, you can simply run git diff without parameters, it will reveal the conflicted regions.
To resolve such conflict, you have to decide which branch has the right content. You can do that by checking out the file from the appropriate branch, for example:
git checkout name_of_branch path/to/file
Sometimes the right content is a mix of the two files. In that case you have to resolve manually, possibly by studying the differences using the git diff command, as in the examples above.
The long-term solution is to avoid making conflicting changes to the same paths in different branches, which is typically a task sharing / communication issue between collaborators.