To run a program you merely type in its name. Many programs accept further information on the command line which modify their behavior.
Most commands take arguments and sometimes commands have several options or parameters available.
The brackets around the parameters indicate they are optional. For example, if you want to see the names of the files in the current directory, the ls command is used. But if you want to view the connects of your public directory while in your home directory, the directory name, public , must be supplied as an argument. These options generally precede other arguments, but this is not always the case. It depends on the the specific program you are using.