Interestingly enough, as a newbie you will not need to use any of the methods you asked about for quite some time. Forced reps, supersets, and dropsets are all intermediate-advanced techniques that should not be employed until you have at least 1-2 solid years of training behind you. Still, I'd be happy to clarify each for you so that when you are ready you will be able to begin adding these techniques to your workouts.
• forced reps: this is when a training partner or spotter applies just enough pressure to a bar or dumbell (cable or machine) to allow you to complete a repetition that you would have been unable to perform on your own due to muscular failure.
• superset: this is when 2 exercises are performed back to back with no rest in between. A rest is only taken upon completion of the 2 exercises. Supersets can be performed for antagonistic bodyparts...chest/back (bench press/lat pulldown) or, for the same bodypart...two tricep exercises in a row (pushdowns/skull crushers).
• dropset: this is when you perform an exercise to muscular failure, then, immediately take some weight off the bar or machine (or grab lighter dumbells) and continue with the exercise. For example, if you are bench pressing with 185 lbs and reach failure, you may drop the weight immediately to 135 lbs and get as many more reps as you can.