spoocter:
As i understand, when i want to output MIDI from the arduino i should connect it with the IN midi jack.
I would think that the OUTPUT from the Arduino would go to the MIDI OUT plug which I expect is normally plugged into the MIDI OUT jack of an instrument. This plug is wired to the I+/I- holes because the OUTPUT of the instrument is the INPUT to the converter.
If your MIDI-to-USB has six holes on the MIDI side I would wire it just like the diagram.
Hole 1 (nearest the LED) through 220 Ohm resistor to +5V or Arduino.
Hole 2 to TX on Arduino
Hole 3 to Ground on the Arduino
If you want to power the Arduino from the USB cable you will need to connect the +5 pin of the USB side to +5V (not Vin!) on the Arduino. Note: The 5V from USB is not sufficient for the Vin pin which needs 7V or more.