writing commands

[Carrie Baker]

The documentaion I am writing includes commands

The user has  to type commands and fill in paramters which change
according to their local settings

e.g.
"command x unit_type serial_numeber"
when unit type is the type  of unit, either x, y or z and the serial
number is the number stuck on the back of your unnit

What is the best way of writing the syntax here, where do I explain
what should go in each of the fields in the command?


-- 
Carrie Baker
carriebak at gmail.com