HIIT really is pretty basic.
Basically you choose two intervals, one shorter and one longer. Common ones are 30 sec/1 min, 1 min/2 min, 20 sec/40 sec (high intensity/low to moderate intensity) During the high intensity you go all out as hard as you can. During the low to moderate you recover from that. On a treadmill it would look something like sprint for 30 seconds, recovery jog for 1 minute. If you don't have a treadmill you can do something like jumprope for one minute and walk or jog for 2 minutes.
I do HIIT with a variety of things,
kettlebells (15/15 sec is typical if you're trying to improve Max V02 or 20/10 sec is Tabata Style and is usually a painfully short and sweet workout! LOL)
Gazelle (1 minute as fast as I can go and 2 minutes recovery pace)
Jump rope and hula hoop (1 minute jump rope, 2 minute recovery hula hooping)
If you run (I don't) then you can really make it easy on yourself and sprint from one block to the next and then recovery jog the next block, and so on.
Start with a short warm up and then try three rounds and a short cool down. It doesn't sounds like much but if you do it right then you will be wiped out! LOL As you adjust then you can add another round or two.
Have fun!!