It is there in the code you linked to.
The function just sets pins (turns on LED's) depending on the num needed.
void mask(int num, int aa, int bb, int cc, int dd, int ee, int ff, int gg)
{
switch (num)
{
case 0 :
digitalWrite(aa, HIGH);
digitalWrite(bb, HIGH);
digitalWrite(cc, HIGH);
digitalWrite(dd, HIGH);
digitalWrite(ee, HIGH);
digitalWrite(ff, HIGH);
digitalWrite(gg, LOW);
break;
case 1 :
digitalWrite(aa, LOW);
digitalWrite(bb, HIGH);
digitalWrite(cc, HIGH);
digitalWrite(dd, LOW);
digitalWrite(ee, LOW);
digitalWrite(ff, LOW);
digitalWrite(gg, LOW);
break;
case 2 :
digitalWrite(aa, HIGH);
digitalWrite(bb, HIGH);
digitalWrite(cc, LOW);
digitalWrite(dd, HIGH);
digitalWrite(ee, HIGH);
digitalWrite(ff, LOW);
digitalWrite(gg, HIGH);
break;
case 3 :
digitalWrite(aa, HIGH);
digitalWrite(bb, HIGH);
digitalWrite(cc, HIGH);
digitalWrite(dd, HIGH);
digitalWrite(ee, LOW);
digitalWrite(ff, LOW);
digitalWrite(gg, HIGH);
break;
case 4 :
digitalWrite(aa, LOW);
digitalWrite(bb, HIGH);
digitalWrite(cc, HIGH);
digitalWrite(dd, LOW);
digitalWrite(ee, LOW);
digitalWrite(ff, HIGH);
digitalWrite(gg, HIGH);
break;
case 5 :
digitalWrite(aa, HIGH);
digitalWrite(bb, LOW);
digitalWrite(cc, HIGH);
digitalWrite(dd, HIGH);
digitalWrite(ee, LOW);
digitalWrite(ff, HIGH);
digitalWrite(gg, HIGH);
break;
case 6 :
digitalWrite(aa, HIGH);
digitalWrite(bb, LOW);
digitalWrite(cc, HIGH);
digitalWrite(dd, HIGH);
digitalWrite(ee, HIGH);
digitalWrite(ff, HIGH);
digitalWrite(gg, HIGH);
break;
case 7 :
digitalWrite(aa, HIGH);
digitalWrite(bb, HIGH);
digitalWrite(cc, HIGH);
digitalWrite(dd, LOW);
digitalWrite(ee, LOW);
digitalWrite(ff, LOW);
digitalWrite(gg, LOW);
break;
case 8 :
digitalWrite(aa, HIGH);
digitalWrite(bb, HIGH);
digitalWrite(cc, HIGH);
digitalWrite(dd, HIGH);
digitalWrite(ee, HIGH);
digitalWrite(ff, HIGH);
digitalWrite(gg, HIGH);
break;
case 9 :
digitalWrite(aa, HIGH);
digitalWrite(bb, HIGH);
digitalWrite(cc, HIGH);
digitalWrite(dd, HIGH);
digitalWrite(ee, LOW);
digitalWrite(ff, HIGH);
digitalWrite(gg, HIGH);
break;
}
}