Because files in IPFS are content-addressed and immutable, they can be complicated to edit. Mutable File System (MFS) is a tool built into IPFS that lets you treat files like you would a normal name-based filesystem — you can add, remove, move, and edit MFS files and have all the work of updating links and hashes taken care of for you.

MFS is accessed through the files commands in the IPFS CLI and API.

This video also provides a good overview of MFS:

Intro to Files API