To clear up the fusions here is a list of fusions!

Gotenks

the fusion result of Goten and Trunks, can reach SSJ3 level. Gokou taught the fusion technique so that the boys can have a chance to defeat Buu, but it turned out that Gotenks was still no match for Buu.

Gozita (Gogeta) (Gogita)

(from Movie 12) the fusion result of Vegeta and Goku. In DBGT, Gozita was formed again when Super Gokou 4 fused with Super Vegeta 4.

Vegetto (Bejito)

fusion of Gokou and Vegeta fused when each wore one of Dai-Kaioushin's special earrings on opposite ears. Vegetto was able to stand up to Boo, but allowed Boo to absorb him anyway to rescue their comrades still inside of Boo's body and so that the effects of the permanent fusion would be cancelled.