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pasted as is from Wiki
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https://www.arduino.cc/en/Main/Software
Select the type of Board you have under Tools > Board
The Arduino Uno, among other models, will show up in the Port list without issue. The Trinket and a few other models do not need a port specified. Always check the error code near the bottom for details.
If you have selected the wrong port, or the Arduino cannot be contacted, you will see some sort of error populate at the bottom of the window that may look something like this.