ANDY'S ANSWER: A pad does two things - it absorbs the liquid, and the plastic on the bottom provides a barrier to stop any liquid from going through to your garments. If you think that you have seen some blood when you pee, but not yet on your underwear, I would suggest you just use a pantiliner. They are very thin and you cannot tell that you are wearing one, but they are still designed to protect your panties from a light flow.
If you are just starting to get periods, it's important for you to pay attention to what is happening. It's not unusual to have a small period at first and not another one for several months. If you have a journal, you may want to make note of the day that you start and the day that it finishes.
After you have been having a regular period for a year or so, you may want to try tampons, but at this age, I would not recommend it. Learning how to use one takes practise and can be uncomfortable until you learn to use them properly. Also, tampons MUST NOT be left in you longer than 5 hours to be safe from the risk of bacteria causing toxins in your body (Toxic Shock Syndrome). Also, even when your periods are regular and heavy enough to warranty a tampon, you'd still want to wear a pantiliner to protect your underwear from possible leakage during your period.