To add to what other people have said, you will see the syntax that the blogger used in their post quite often.
There are pretty consistent standards that are used when writing documentation on how to use commands. In every manual page, you'll see pretty much the same structure.
If something is optional, it is usually in brackets.
ls [folder] (you don't need to give ls a folder, but you can. Thus, optional).
If something is a file or email, you will usually see it in angle brackets.
If you have an choice between a finite number of things (i.e Months), you'll see it in braces like this:
With any one of these, you may see
... which denotes that multiple of this can be given.
And finally, if something is absolutely mandatory, you'll see its documentation listed out and probably underlined. For instance,
man mv, mv's manual, says this:
mv [OPTION]... [-T] SOURCE DEST
Technically speaking, the package name (write) isn't a required part of the command. Try it.
apt-get install or
apt-get remove will just run and exit the program successfully. That's one reason it could be presented in brackets on that blog.