Hello I'm new here and I want to ask you something for my project. My project is like a Nintendo DS and I use two arduinos: one for the joystick shield and one for the tft display. How can I connect them it would be really nice if you send a code too.
That's an original and interesting idea for a project!
I don't think anyone has tried what you want to do. So unfortunately no-one will have any useful code to share.
It's better if you start your project and then ask questions when you get stuck.
You could connect two arduinos by SPI or I2C, or maybe serial. It depends what kind of data you need to send and what else is happening on the system. You've described a display and a joystick - will there also be some kind of game software running somewhere?
Thanks! I will try it when the TFT arrives 
Frankly, your question is rather muddled.
A Nintendo DS specifically provides two screens, that is what the "DS" means.
There is no need to use a separate Arduino merely to service a joystick and buttons. In general, it is poor design to use two separate Arduinos in the one assembly because you then have to implement a communications protocol to synchronise their operations and that takes significant code space and processing time.
It just might be appropriate to have two separate Arduinos to service two TFT displays, and it might be required to use Mega 2560s to conveniently drive such displays. All these are important design considerations.