Did you buy the Thai Kitchen brand? It is by far my favorite, and I have tried a lot of different Pad Thai sauces.
Just follow the recipe on the box, and experiment. The beauty of it is you can adjust the recipe to your liking by adding more of this or less of that.
For the noodles, boil the water, put the noodles in, remove from heat and let them sit covered for about three minutes. You don't want to fully cook them, but let them be very al dente. Remove and rinse with cold water and set aside.
I like to stir fry up some tofu and veggies (broccoli, purple cabbage, green onion, garlic, etc.) in oil. Sometimes I add some soy sauce and a little Pad Thai sauce to the veggie mix. Then dump in the noodles (partially cooked) and sauce and cook until it seems ready.
I find that when I add all the extra veggies and stuff, I really need more sauce than what comes in the box. They sell the sauce separately in a jar, so get some of that.
I doctor up the sauce with fresh lime and Vietnamese garlic chile sauce, the kind in the clear plastic jar with a green lid. Rooster sauce will do. I like to scramble the eggs separately and sort of fold them in near the end. I like lots of egg in mine.
When it's done, I add a lot of crushed peanuts and serve with mung bean sprouts, lime and more garlic chile sauce.
I use the Cooks Illustrated recipe. It is EXACTLY what you get in a restaurant. There are two key ingredients or steps in this recipe that make it work. The first is the tamarind paste or tamarind thai soup base that goes into the sauce. I've used both, and both produce a good flavor, but the paste is more concentrated in flavor than the soup so you need less of it. (If you like to make sweet and sour soup, get the soup base). The second key step is frying the shallots with the egg.
Be prepared to shell out some money the first time you make it. Once you have the tamarind and fish sauce and other things in your kitchen, it is fairly simple and inexpensive to make.
I like to serve it with green papaya salad and thai iced tea - there are excellent versions of these on the Food Network website.