Callbacks offer a mechanism to incorporate custom logic into different components of CPQ, such as line items, cart pages, and catalog pages, during runtime. For instance, you can apply custom pricing or validation to line items within the cart using Pricing Callback Classes and Validation Callback Classes respectively. Implementing callbacks involves utilizing interfaces tailored to each specific callback. It's essential to implement these interfaces in C# and configure your custom logic within the corresponding class using the interface's methods. Subsequently, after implementing the interface, you need to register the C# class on the platform to enable invocation of the callback class during runtime.