you can trans when ur CF bar is full (remember, this is when turbo is NOT on) or you can have a look at the character descriptions (when ur choosing which character to play as) to see what lvl they can trans. Once your trans you get an "ultimate" pl (apart from cell and krillin) this means you can turn ssj, etc.. instantly (by the way, you can defrom by pressing x, this comes in handy if your transforming and you see someone swooping for you, or if you want to use a lvl 1 attack, for example spirit bomb)