There's a number of ways of doing it, time/ distance etc. Time being the most popular
And yes, you're meant to sprint flat out. Try and build your self up to it with some strides first, and build up to sprints over a couple of weeks. Then the fun begins, because the better you get at them the harder you're able to sprint and the longer you're able to keep the intensity up for
It's a mistake to jog for 15-20 minutes before hand though, warm up by doing a very light jog for ten minutes or so, some strides, and then bang into it hard.
I used to do them years ago while helping out a mate for his boxing. We'd get up at 5, do our sprints, I'd go off to work he'd head home to bed........ :blink: