Объясните кусок кода - Pascal ABC

var a:array[1..20] of integer;
    i,j,n,m,c:integer;
begin
  writeln('Элементов:');readln(n);
  for i:=1 to n do
  begin
    writeln('a[',i,']=');readln(a[i]);
    end;
    for i:=1 to n-1 do
    begin
      m:=i;
      for j:=i+1 to n do
        if a[j]<a[m] then m:=j;
        c:=a[i];
        a[i]:=a[m];
        a[m]:=c;
       end;
       for i:=1 to n do writeln(a[i]:3);
end.

c:=a[i];
a[i]:=a[m];
a[m]:=c;