The protagonist is a single character in a story (typically; though some instances like Cloud Atlas subvert this). Plural-protagonist means each of the protagonists have mutual desires and succeed together. Multiprotagonist means characters have individual desires. These typically occur in multiplot stories, in which smaller stories are woven together. Some stories, like Psycho switch protagonist part-way through. Protagonists are willful and active. They have a conscious desire, and must be given a chance to attain it. They must be empathetic (but not necessarily sympathetic); they must be at least relate-able on some level. This hooks the audience to the story of the protagonist.
Risk: What does a character stand to lose if they do not get what they want? the measure of value of any desire is in proportion to the risk involved in its pursuit.
Writing from the inside out: we must place ourselves in the character's point of view. Ask yourself 'if i were this character in these circumstances, what would I do?'
McKee emphasizes the importance of making reactions unexpected by the audience, otherwise they don't need describing. He uses the example of writing as part of a screenplay someone walking up to a door, knocking, and then the door being opened to let them in. It is natural and expected, and just creates dead time on screen. It can be skipped for the character just being shown already inside the house.