Instructions
Visit online walkthrough and FAQ repositories, such as GameFAQs and IGN FAQs. Both host walkthroughs, some of which have considerable detail. The main appeal of these walkthroughs is that they're free. The drawbacks are that they don't usually have images and they're online, so you may need to run back and forth between your gaming console and your computer.
Visit a gaming store to find a copy of one of the printed guides. There are two such guides for "Super Paper Mario," Nintendo's official guide and an unofficial Prima guide.
Purchase one of the guides from an online book retailer. Since "Super Paper Mario" was released in 2007, you may not be able to find a guide in your local gaming stores. You can also look on auction sites for a used copy.