Branches and merges

Branch = label

        D --- E   (feature)
       /
A --- B --- C   (main)

git switch feature moves your working copy; main stays parked at C. Commits on a branch don't affect main until you merge — cheap experimentation is the whole point.

Merge = two-parent commit

        D --- E
       /       \
A --- B --- C --- F   (main, after merge)

F has both C and E as parents; the histories join. When both sides edited the same lines differently, git refuses to guess — a conflict. Resolution is a human decision recorded in the merge commit: keep theirs, keep yours, or write the version that's actually correct. Conflict markers (<<<<<<<, =======, >>>>>>>) mark the two candidate texts; delete the markers, keep the intended code, stage, commit.