A superset is when you perform two exercises back to back with no rest in between the exercises. There are many types of supersets that you can do, but for this article let's keep it simple and quick since it's the holidays.
During your restance training workout, instead of taking a 45 second break or so between sets, just keep moving by doing an opposite muscle group during your rest period.
For example, if today is your Arms and Shoulders day, you can work your biceps during your tricep break and/or work your arms during your shoulder break. If it's leg day, workout your hamstrings (back of your leg) during your quadricep break (front of your leg). This will ultimately help to increase the intensity or your workout (therefore, burning more calories), and also increase your heartrate (cardio).
Remember, you'll have no breaks in between sets during supersets, so stay focused, pay attention to form, and monitor your heart rate. Your maximum heart rate is always 220-your age in beats per minute. That means that if your 40 years old, and your heart is beating 180 beats per minute, you've reached your max, and need to slow down or stop for a while and catch your breath.