$ git --help
git [--version] [--help] [-C <path>] [-c <name>=<value>] [--exec-path[=<path>]] [--html-path] [--man-path] [--info-path] [-p | --paginate | --no-pager] [--no-replace-objects] [--bare] [--git-dir=<path>] [--work-tree=<path>] [--namespace=<name>] <command> [<args>]
These are common Git commands used in various situations:

start a working area (see also: git help tutorial)
clone      Clone a repository into a new directory
init       Create an empty Git repository or reinitialize an existing one

work on the current change (see also: git help everyday)

add        Add file contents to the index
mv         Move or rename a file, a directory, or a symlink
reset      Reset current HEAD to the specified state
rm         Remove files from the working tree and from the index

examine the history and state (see also: git help revisions)

bisect     Use binary search to find the commit that introduced a bug
grep       Print lines matching a pattern
log        Show commit logs
show       Show various types of objects
status     Show the working tree status

grow, mark and tweak your common history

branch     List, create, or delete branches
checkout   Switch branches or restore working tree files
commit     Record changes to the repository
diff       Show changes between commits, commit and working tree, etc
merge      Join two or more development histories together
rebase     Reapply commits on top of another base tip
tag        Create, list, delete or verify a tag object signed with GPG

collaborate (see also: git help workflows)

fetch      Download objects and refs from another repository
pull       Fetch from and integrate with another repository or a local branch
push       Update remote refs along with associated objects

git help -a and git help -g list available subcommands and some concept guides. 
See git help <command> or git help <concept> to read about a specific subcommand or concept.