Conflicts

When two sides changed the same lines.

What causes one

Git merges different regions of a file on its own. It stops and asks only when both sides changed the same lines, because it has no way to choose.

A conflict is a question, not a failure.
Markers show your version, the incoming version and where they meet.

Resolving

Edit the marked region until the file reads as it should, delete the markers, then git add the file and commit. git merge --abort backs out entirely if you would rather start again.