How long does Blink run for?
Once you have Blink running. Try this experiment:
Unplug your Arduino, wait a few moments and plug it back in. Is Blink still running on your Arduino (LED blinking on and off once every second)?
Walk away from your computer and go have a cup of tea. Then come back, is Blink still running?
Now go to sleep for 8 hours, wake up and eat breakfast. Then check back on your Arduino, is Blink still running?
Aspire to become a monk. Leave your home with only the clothes on your back and an Arduino in your pocket. Travel the world for 10 years, learning about yourself and the depth of your own existence. In a distant land, find a power plug or USB cable and plug in your Arduino, is Blink still blinking?
The answer is (and would be if you had 10 years): yes! Blink will run essentially forever on your Arduino. It isn't like an app you have to launch or upgrade. The Blink program is saved into the FLASH storage of the chip, which is like a very very small USB key. Even if you lose power and forget about your Arduino for years, you can plug it back in and it will run the same sketch it did last time.
What does the Reset button do?
While looking at the LED, hold down the Reset button? What happens to the LED? It should have stopped blinking. Holding down the reset button will halt the Arduino temporarily.
While looking at the LED, release the Reset button. You'll see a quick triple-flash from the Arduino and then it will return to turning on and off the LED once every second