What is pizza sauce?
Pizza sauce is, presumably, whatever tomato-based sauce you'd put on a pizza. Those tend to be essentially like smooth (not chunky), lightly seasoned spaghetti sauce. If by "plain tomato sauce" you mean a jar of tomato sauce for spaghetti, you're probably in good shape. If you mean a can of pure tomato sauce, with no other ingredients, you'll probably want to add some seasoning. Basil and oregano are good bets for herbs; garlic and onion are also common, and perhaps crushed red pepper if you want a little kick.

If you're looking for a real recipe, this isn't a recipe request site, but search engines will serve you well.