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See my answers below for each question:
1. Yes, the DS2 is the on-board LED and it is connected to the IO13. If you toggle the IO13 and has an external LED connected to this pin, then both LEDs will blink.
2. That's an error in the image. The positive strip connected to the 5V pin is not used in the Blink example. You can ignore it.
3. The 5V pin is not used, so there is no need to connect the positive strip.
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