Sensory information about your situation passes through the thalamus and cerebrum for interpretation. The cerebellum helps you process both the language you are hearing and speaking but also the motor movements necessary to begin speaking.
Work Step by Step
You can give varying levels of detail, but this is a high overview. To begin speaking, you need to take in your surroundings, read and understand your notes, process the situation, process what you will say and how, and actually make the movements necessary to speak. You could give additional layers to this involving emotional processing or memory.