Could you explain to me the life course for a massive star (30-40 solar masses) from birth to death using the HR Diagram (by showing key events in its life)?
I won't primarily explain the H-R diagrams, because I think focussing on some of the underlying physics is essential for understanding, especially stellar nucleosytheses. For simplification let's assume the star initially consists of nothing else than ordinary hydrogen and traces of carbon and nitrogen.
Nuclear fusion of hydrogen forms helium; fusion of helium forms carbon; fusion of carbon leads to heavier elements like neon, also oxygen, sodium, magnesium; neon decays to oxygen; oxygen fuses to silicon and others; silicon fuses stepwise with helium to iron. Each of these phases of burning needs higher temperature, and it releases energy. The phases can be subdivided in first core burning, then shell burning.
Earlier phases last long enough to be be visible from outside, resulting in motion within the HR diagram. Heating from phase to phase generally results in an overall expansion of the star. The last phases last only a short time, too short to propagate effects to outside.
Fusion of iron consumes energy. Therefore the star gets a problem after the core consists of iron. Outer pressure cannot be stopped by fusion and further heating: The core collapses to a neutron star or a black hole, while the outer part is blown off by a supernova. Neutron stars usually rotate rapidly, and cool down over very long periods of time.
After this overall framework you may go deeper into details of the phases.