Gokuu is now an adult and will meet his destiny.
First arc:
Saiyajins & FreezerRaditz tells Gokuu of his true origin as a Saiyajin. Gokuu refused to join him, so Raditz kidnaps Gokuu's son,
Gohan. Gokuu sacrifices his life to win the battle.
Vegeta &
Nappa come down to Earth but are defeated. Vegeta retreats to one of
Freezer's command posts. Gohan, Bulma, and Kuririn get in Kami-sama's old spaceship and head off towards Namek to collect their Dragon Balls.
Second arc:
Jinzouningen & CellThe plot centers on 4 jinzouningen who were built to kill Gokuu and fight everyone who tries to protect him.
Cell, one of the 4 jinzouningen, absorbs 2 of the others to become capable of destroying the universe. Gohan, is the only one who can stop him since he has been shown to be more powerful -- and faster -- than his father.
Third arc:
BuuBuu is the new threat to Earth, and he turns people into candy to then eat them.
Note regarding the US/R1 version and any version based on it (informally, the "US chopjob"):The first 80 episodes of DBZ were cut down to 65. For a listing of the episodes scroll down to the "O" specials and read their episodenames. All other episode were not cut together.