In the command line or Script Editor, type help <command name>, for example:
help move
Show the Maya Help for a command.
Go to the Help menu and select MEL Command Reference.
Display auto-completion results for commands and object paths as you type them in the script editor
In the Script Editor, turn on Command > Command Completion and Object Path Completion. Then type the first few letters of a command and press + , or turn on Command > Show Tooltip Help to display auto-complete options automatically.