Ideation is the act of thinking more broadly about the problem without considering the development contraints, it ensures that we are building the best possible solution, not just one that seems good enough.
Personas are imaginary yet realistic and detailed descriptions of the primary users of your product, it helps in creating a consistent interface of the product.
Scenarios and storyboards provide a reality check for the designs, helping us identify design gaps and articulate exactly what features we need to build to make users happy.
These techniques ensure that the design ideas we have are workable, show us what types of interactions will be required, help us to explore what error conditions might exist, and help to predict how users might interact with the interface. This all happens before we do any actual interface design.
Prototyping helps us in validating our ideas before we write any code. It put together the elements of our new elements design in a way that approximates what users will see on screen.