Git is a distributed version control system. It means it not only support a central repository to do check-in or checkout however at every client machine you can do exactly same version control operation as what you do with the central sever.
The major difference between Git and other version control system like CVS, SVN and TFS is that all other version control system keeps track of file base changes per commit(what are all files changed and what changed in those files per check-in or per commit level) and while GIT keeps snapshot of whole file system at per commit level. If there is no change in some files per commit level then it will only point to those files as reference. So that means per commit GIT keeps track of all state of all the files available at per commit level.
All operation are local. Right from check-in or commit a file to pull history to branching, etc can be done locally without connecting to a network.
Other version control storage mechanism
GIT Storage Mechanism