Those are options which are explained in the man page
EXAMPLE:

Code:

The following options can be used with ps:

  -a  Prints information to standard output about all processes, except the
      session leaders and processes not associated with a terminal.

  -A  Writes information for all processes.

  -d  Prints information to standard output about all processes, except the
      session leaders.

Specifiers are explained in the ps man page
EXAMPLE:

Code:

Format Specifiers


  The following list contains all format specifiers that can be used with ps:

  ________________________________________________________________
  Specifier   Header	Meaning
  ________________________________________________________________
  acflag      ACFLG

			[Tru64 UNIX]  Process accounting flag
  args	      COMMAND	Command arguments
  c	      C		CPU utilization factor for scheduling

what does [=header mean] ?
RTM - it should be apparent by now....

From the ps man page:

Prints only information about processes that are in the process groups
listed in glist. The glist is a list of process-group identifiers
enclosed in " " (double quotes) and separated from one another by a
comma or one or more spaces (or tabs), or both.


The ulist argument is either a list of
user IDs or a list of user IDs enclosed in " " (double quotes) and
separated from one another by a comma or one or more spaces, or both.

You should really try reading the complete man page and then ask questions about it - all of the descriptions are in the man page (in this case).