Merge them

Create a new change in master

Only to simulate a conflict!

git checkout master

echo "content modified in master" > code.txt

git commit -am "content modified in master"

Merge the branch on master

git merge feature

Results in conflict

Auto-merging code.txt
CONFLICT (content): Merge conflict in code.txt
Automatic merge failed; fix conflicts and then commit the result.

cat code.txt

<<<<<<< HEAD
content modified in master
=======
some content from feature
>>>>>>> feature

Resolve manually

Resolve manually using some file editor (What you keep in the final modification is upto you and the other developer as per situation)

Commit again

After final modification, commit again

git commit -am "merged feature"

git log --oneline

Merging is now complete!