The Specialty Trainee Assessment of Readiness for Tenure (START) assessment is a tool to highlight areas requiring focus for the last leg of your specialist training. It is not an exam.
The START assessment is an opportunity to practice potential consultant interview scenario questions. It is not something you can pass or fail so do not put too much pressure on yourself.
A Wessex trainee has produced a helpful Guide to the START assessment document, which contains information regarding application, structure, and is full of very useful tips.