Can somone explain to me jango's abilty : After an opponent activates a character, you may activate this character.... Does that mean that i can roll his die after opponent activates a character then i have additional action or what?

Yes, when an opponent activates a character you can then activate Jango and roll him in. It is then your action and you can choose to resolve dice or perform another action.

7 hours ago, Cadbane said:

Can somone explain to me jango's abilty : After an opponent activates a character, you may activate this character.... Does that mean that i can roll his die after opponent activates a character then i have additional action or what?

As Jorgyn said its not really an additional action its that Jango activates during your opponents turn. So you have Jango, they go to activate Qui Gon, they finish activating Qui Gon, then you can roll in your Jango before it goes back to your turn. So you can then resolve his and any other dice with the same symbol, say you already had 2 +2 ranged already in play and roll Jangos 1 range you could resolve 5 damage.