The basic idea of the program you're trying to write is:
loop() {
strip.show(); // Turn LED strip on.
delay(1000); // One second, argument is milliseconds.
strip.setBrightness(0); //Turn LED strip off.
delay(5000);
strip.setBrightness(155); //Turn LED strip on.
}
I haven't used the Adafruit DotStar library, so there may be details that I'm missing (like do you need to do a strip.show() after setting the brightness). But maybe this is enough to get you thinking about how to construct the program.
The real joy in hacking with something like this is the experimenting and the learning. Take the time to try to understand how you project works and to predict what will change as you modify the code and how you can tell if it is working the way you expect – that will get you a long way towards being a strong programmer.