The tool App provides two core functions: to quickly convert letters to corresponding numbers (A for 0, B for 1, and so on), and to convert numbers to corresponding letters (0 for A, 1 for B, and so on). Users can easily enter letters or numbers, and instantly get the converted results, convenient and fast. These features allow users to easily and accurately convert between letters and numbers, making them ideal for use cases where such operations are frequently required.