How do I resolve merge conflicts in a Git repository?

Try:

git mergetool

It opens a GUI that steps you through each conflict, and you get to choose how to merge. Sometimes it requires a bit of hand editing afterwards, but usually it’s enough by itself. It is much better than doing the whole thing by hand certainly.

As per Josh Glover’s comment:

[This command]
doesn’t necessarily open a GUI unless you install one. Running git mergetool for me resulted in vimdiff being used. You can install
one of the following tools to use it instead: meld, opendiff,
kdiff3, tkdiff, xxdiff, tortoisemerge, gvimdiff, diffuse,
ecmerge, p4merge, araxis, vimdiff, emerge.

Below is a sample procedure using vimdiff to resolve merge conflicts, based on this link.

1. Run the following commands in your terminal

   git config merge.tool vimdiff
   git config merge.conflictstyle diff3
   git config mergetool.prompt false
   

   This will set vimdiff as the default merge tool.

2. Run the following command in your terminal

   git mergetool
   

3. You will see a vimdiff display in the following format:

     ╔═══════╦══════╦════════╗
     ║       ║      ║        ║
     ║ LOCAL ║ BASE ║ REMOTE ║
     ║       ║      ║        ║
     ╠═══════╩══════╩════════╣
     ║                       ║
     ║        MERGED         ║
     ║                       ║
     ╚═══════════════════════╝
   

   These 4 views are

   • LOCAL: this is the file from the current branch
   • BASE: the common ancestor, how this file looked before both changes
   • REMOTE: the file you are merging into your branch
   • MERGED: the merge result; this is what gets saved in the merge commit and used in the future

   You can navigate among these views using ctrl+w. You can directly reach the MERGED view using ctrl+w followed by j.

   More information about vimdiff navigation is here and here.

4. You can edit the MERGED view like this:

   • If you want to get changes from REMOTE

     :diffg RE
     

   • If you want to get changes from BASE

     :diffg BA
     

   • If you want to get changes from LOCAL

     :diffg LO
     

5. Save, Exit, Commit, and Clean up

   :wqa save and exit from vi

   git commit -m "message"

   git clean Remove extra files (e.g. *.orig) created by the diff tool.