Drone-kit Python is not connecting with Iris+

I’m trying to build my first dronekit python program, and I’m doing some tests with some examples but I couldn’t connect to my UAV(Iris+). I plugged the usb radio(3DR 915 MHz) and I put vehicle = connect('/dev/ttyUSB0', wait_ready=True). Actually I have no idea which string I should put in. Are there any hardware changes that I need to do or so? I just pressed a button until the led became red and then I waited another LED became green and then I plugged the usb radio into my computer.Thanks in advance. Thanks in advance guys, I need some help!