Program: Beginner Needs Help

I'm a student who really needs help.  I am trying to write a program where a cattle rancher will create a file including data about his three groups of cow.  The data includes the color of the cow - black, red, or white; the weight of each cow and the yield of milk the cow produces.  What he wants from this program is the total # of cows in each color group, their average weight and their average monthly yield of milk.  This program must use arrays and procedures and functions.  Also the data is read from a file and an eof function is required.  A set of constants, variables, types, functions and procedures is supplied and must be used.  The output should be to screen in a format similiar to the following:
------------------------------------------------------------
Black Cows                                                10
Average weight in kilograms                            842.3
Average monthly milk yield                             333.3
------------------------------------------------------------
for each group.  I just do not understand how the arrays work and what they do really.  The following is a list of the required constansts, types, variables, procedures and functions:
CONST
 MinWeight = 300.0;  MaxWeight = 799.9; {to validate weight}
 MinMilk = 0.0;          MaxMilk = 399.9;     {to validate milk/m}
 MaxNoOfCowsPerGroup = 50;
 Hypens = ‘-----------------------------‘;             {to separate lines of output}
 DiskNameOfInputFile = ‘CATTLE.DAT’;
TYPE
 ColorType =   (black, red, white); {to be neat and index the Counter
         array and the first dimension of
         Herd by color }
 WeightMilkType =   array [1..2] of real; {pair of real numbers to store the
         weight and milk data of one cow }
 GroupType =   array [1..MaxNoOfCowsPerGroup ] of WeightMilkType;
       {one WeiMilType pair for each of a
         possible maximum of
         MaxNoOfCowsPerGroup cows in a
         color group }
 HerdType =   array [ColorType] of GroupType;
{one GroupType array for each of  
  the three color groups }
 CounterType =  array [ColorType] of integer;
{three integers to count the actual
number of cows in each color group}
 string19 =   string[19];  {this type of variable will hold the
error messages passed from the  input validating routine}
 string[5] =   string[5];  {for ColorOut}
 InFileType =   text;   {type of input fi
       
CONST
 ColorOut:  array[ColorType] of string5 = (‘Black’, ‘Red’, ‘White’);
       {comes handy when labelling the
         output results}
 ColorCode:  array [ColorType] of char = (‘B’,’R’,’W’);
       {to validate color-code and to
         convert code to a ColorType value}
VAR
Herd:   HerdType;   {3-dim array for weight and milk
  data of the herd}
 Counter:  CounterType;  {a counter of the cows for each
         color group}
 InFile  InFileType;  {file variable; internal name of input file}
 i:  ColorType  {index for Counter array and first-dim of Herd}


{************************************************************************}
FUNCTION Convert ( c : char ) : ColorType;
{
  imports: a valid color code, ‘B’, ‘R’, ‘W’
  task:       convert the code into the pertinent ColorType value, black, red, or white
  exports:    the function value, ColorType value pertaining to ColorCode }
{************************************************************************}
  PROCEDURE LoadHerd (var InFile: InFileType; {input file of cattle.data}
                                             var herd: HerdType; {array to hold weight/milk data}
            var counter: CounterType);
       {# of cows in each of 3 groups}
{
  imports:  input file variable, InFile
  input:      color and a WeightMilkType pair for each cow in the herd; from InFile
  task:        it handles all input tasks, including assigning and resetting InFile.  It reads
in and validates data for each cow until the end of InFile is reached.  Valid
data is stored in the 3-dimensional array Herd.  The first dimension
segregates the cows by color, the second dimension distinguishes
individual cows within a color group, and the third dimension discerns
weight and monthly yield of milk.  The cows in each color group are
counted by array Counter.  If invalid input data is detected, then it displays
an appropriate error message, and ignores the invalid data line.
  exports: InFile (position pointer at eof mark)
  Herd, filled with weight/milk data
  Counter, giving the # of cows for each color group
output:  if invalid data is detected, then one of three types of error messages is sent
  to the screen
{************************************************************************}
PROCEDURE Validate ( color:char;     {value parameter for color code}
                                         WeiMil:WeightMilkType; {value parameter for weight & milk}
                                          var ERROR:string 19);  {exports an error message or "}
{
imports:          data of a cow, in color and WeiMil
task:                validates color, weight, and milk.  If all are valid, then ERROR exports
                        the null string (ERROR := "); Otherwise, ERROR exports one of the       
                        following error messages: ‘invalid color code’
                                                                  ‘out of range milk/m’
                                                                  ‘out of range weight’
exports:           an error message if input error is detected; the null string otherwise.  }
 

{************************************************************************}
PROCEDURE PrintAverages ( cows: GroupType; n integer );
{
imports:        weight and milk/m data of a group; and number of cows in the group
task:              computes average weight and milk\m, and produces five lines of display:
                     a line of hyphens
                     a line reporting the number of cows
                     a line reporting the average weight of the cows
                     a line reporting the average monthly yeild of milk
                     a line of hypens.  }

Thanks a lot, Shelly