Git merge is a command that combines multiple sequences of commits into one unified history. It is used to integrate the independent lines of development created by git branch and merge them into a single branch. When merging two branches, git merge takes two commit pointers, usually the branch tips, and finds a common base commit between them. Once Git finds a common base commit, it creates a new "merge commit" that combines the changes of each queued merge commit sequence.

If Git encounters a conflict during a merge, it will edit the content of the affected files with visual indicators that mark both sides of the conflicted content. These visual markers are "<<<<<<<", "=======", and ">>>>>>>". Its helpful to search a project for these indicators during a merge to find where conflicts need to be resolved.

To perform a merge, you can run the command "git merge <name of the branch to be merged>". If the merge stops due to conflicts, you can conclude the merge by running "git merge --continue". Merge conflicts happen when both branches you’re trying to merge change some part of the same file. To solve merge conflicts, you need to understand what caused the conflict and decide which version of the code to keep.