Is it normal for girls to have huge blood clots on their period ?

No, first days can: benfairly heavy w/ need to change pads every 2 - 3 hours, but large clots are unusual, and I recommend that you discuss this with your doctor, who may want to check you for anemia, bleeding tendency or hormone imbalance, or if sexually active, a spont abortion. If you are lightheaded or dizzy or if your period has been more than 1-2 days, then I recommend that you go to urgent care or ED.

Yes, it can be.: The "bleeding" at the time of a period comes from the sloughing of the unused uterine lining which builds up each month in preparation for pregnancy. When no pregnancy occurs, this lining comes out, as what we see as menstrual "bleeding." So depending on the amount of the lining, it can appear that there are "huge clots." If you have a concern about a heavy period, please also ask your doctor.