How do you get fusions in Dragon Ball Z Budokai Tenkaichi 2

You can't get fusions. You can fuse items though. If you want to fuse characters all you need to do is have 3 blast stocks and do L2 + right directional button + R3. This lets you do the fusion dance. To do the potara fusion, you must have also 3 blast stocks and do L2 + left directional button + R3. But you must have the right characters ( i.e. Goten and Trunks, Goku and Vegeta)
Note: This is for PS2