Try to explain what the first sub of https://gist.github.com/asciidisco/cb094eadfb4c590e2701 does

gistfile1.pl

sub HMLAN_Initialize($) { # sub takes only one argument
  my ($hash) = @_; # takes all arguments provided during the sub routine call and shoves them into $hash
 
  require "$attr{global}{modpath}/FHEM/DevIo.pm"; # gets another perl module involved (need to check this for function definitions as well)
 
# Provider
  $hash->{ReadFn}  = "HMLAN_Read"; # basically assigns values to the attributes provided to the sub routine call
  $hash->{WriteFn} = "HMLAN_Write";
  $hash->{ReadyFn} = "HMLAN_Ready";
  $hash->{SetFn}   = "HMLAN_Set";
  $hash->{AttrFn}  = "HMLAN_Attr";
  $hash->{Clients} = ":CUL_HM:";
  my %mc = ( # creates an associative array (hash) with a single value for now
    "1:CUL_HM" => "^A......................",
  );
  $hash->{MatchList} = \%mc; # again, assigns to params provided to sub routine
 
# Normal devices
  $hash->{DefFn}   = "HMLAN_Define";
  $hash->{UndefFn} = "HMLAN_Undef";
  $hash->{AttrList}= "do_not_notify:1,0 dummy:1,0 " .
                     "loglevel:0,1,2,3,4,5,6 addvaltrigger " . 
                     "hmId hmKey hmKey2 hmKey3 " .
                     "respTime wdStrokeTime:5,10,15,20,25 " .
					 "hmProtocolEvents:0_off,1_dump,2_dumpFull,3_dumpTrigger ".
					 "hmLanQlen:1_min,2_low,3_normal,4_high,5_critical ".
					 "wdTimer ".
					 $readingFnAttributes; # apparantly just a long, concatenated string of attributes
}