The dragonballs are 7 yellow, magical balls with stars on them. Once these
balls were gathered together by someone and a password was issued to it, the
eternal dragon would come out and grant almost any wish that the person
would ask. There are three different sets of dragonballs, some with different
rules...

The Namek Dragonballs:

Three wishes can be granted.

Password must be issued to the dragonballs in namekin language or
the dragon will not come to grant wishes.

Wishes must be in namek-jin language.

The Earth Dragonballs:

One wish can be granted.
a password must be said.
After wish is made, the dragonballs scatter around the world again.
Cannot be used again for one year.

The Dark Start Dragonballs:

One wish can be granted.

After wish is made, the dragonballs scatter across the universe. The
balls must be found and gathered again within one year or else the
planet that wishes were made on will be ultimately destroyed unless the balls return within one year.