Version control systems allow you to record the history of files and share files among several computers and collaborators in a professional way. Especially when working with software development or technical writing, it is essential to have file changes documented and to ensure that every computer and person involved in the project have the most recent updates of the files.
Projects that you want to share among several computers or project workers are most conveniently stored at some web site "in the cloud", here called project hosting services. For efficient access to the files, and the possibility to work offline, you interact with local copies of the files on your computers. I strongly recommend you to use such sites and version control for all serious programming and scientific writing work.