When merge is performed there are three states that are involved: our latest changes, their latest changes and the base node
The base node is the first common ancestor for both the branches (The point at which the code diverged)
Git finds the base node and compares our code and their code with it and based on the comparison shows the conflicts that need to be fixed manually

git merge <branch-name>
 
git merge --continue
# Won't prompt for Merge Message
git merge --continue --no-edit
 
# Abort an merge
git merge --abort

IMPORTANT

We need to be on the target branch when we are trying to merge another branch

Resolving Git Conflicts from the Command Line

How do I finish the merge after resolving my merge conflicts? - Stack Overflow