Subcommands take options and start with --.
You can view all the options and their purposes by running aws <command> <subcommand> help.
While most are optional (hence the name), those that are not surrounded by square brackets ([]) are required. You will get an error message (with the appropriate details) if you don't include them.
The built-in documentation is the best place to start looking for answers. There are usually examples after all of the options have been described. Otherwise, there are plenty of examples available online.
Some options are available for all or most commands, so they are particularly useful to know.