Activating keyboard keys with Arduino

Iam trying to make a button that can activate keys on my keyboard, but i cant find any code. I found a keyboard library but its not for the UNO. Also didnt find any code for processing, as that may help. Any tips or help?

make a button that can activate keys on my keyboard

Would you please give a bit more information on what you are trying to do?

I want to make a button that, when i press it, activates a key on my keyboard: for example when i press the button the f12 key gets activated. I want this for a dj setup where i dont want to have to go to my laptop every time i want to start or stop a recording (since there is no such button on a dj controller). I thought of starting a javascript when the button is pressed but i dont have any java experience and i dont know if this is possible either. Help would be very much appreciated. :)