What do I have to watch first?¿?¿?¿? Help!¡!¡!¡!¡?¿?¿?¿?

Well "Kai" is DBZ it's just repackaged as kai for whatever reason. Well آپ could start with Dragon ball for Goku's childhood and backstory (it does come up in some eps.) but it is not a prerequisite for understanding the show. Here is the saga in order.
1. Vegeta/ Saiyan Saga
2. Freza/ Namek Saga
3. Garlic Jr. Saga
4. Trunks/ Android Saga
5. Cell/ Cell Games Saga
6. World Martial Arts/ Gohan Saga
7. Majin Buu Saga

I have to say the دکھائیں has one of the campiest endings ever, whats sad is it was in the manga, so its legit :( Dragon Ball GT follows it but isn't considered cannon, its also in my opinion pos. But feel free to watch it. Oh also episode wise...
DB- about 130 eps.
DBZ- just under 300
DBGT- about 67 I think...

hope that helps!