Like all stars, high-mass stars are formed from a mixture of gas and dust. High-mass stars are born from a particularly dense amount of this mixture; the high density makes it possible for a high-mass star to come into existence. When a lump of this mixture gets dense enough, gravity causes more gas and dust to congeal onto it, eventually forming into a star. Once the temperature reaches a high enough level for nuclear fusion to begin, a star is born.
The life of a star is measured in the time it takes for it to run out of hydrogen, which is extinguished during nuclear fusion. Nuclear fusion is the process of taking two hydrogen atoms (one proton each) and forming a helium atom (two protons), and this occurs in the core of a star. Once a star has more helium than hydrogen, it begins to collapse in on itself because helium is heavier than hydrogen. The more massive a star is, the faster it extinguishes its hydrogen, and thus high-mass stars have relatively short lives. Some high-mass stars only last a few million years; in cosmic terms, this is very short (in comparison, the sun, an average-sized star, will have a 10 billion year lifespan).
High-mass stars burn out quickly, but they do not die quietly. As the helium causes the star to condense in the core, more massive elements of matter are created, starting with oxygen and carbon, and then eventually sulfur and silicon (indeed, all known elements in the universe are believed to have been formed from high-mass stars). Eventually the core of a high-mass star becomes iron, and it is at this point that the star is too dense to continue to survive. The result is a supernova, which is when the star explodes and sends its matter out in waves.
There are several possibilities for the afterlife of a high-mass star. After a supernova, the material that was projected out has a possibility of forming a nebulae, which is a mix of the material that was projected out from the dying star. A nebulae is a prime location for gas and dust to congeal into a new star, thus dead high-mass stars are recycled into new stars. The core of a dead high-mass star is a candidate to become black hole, which is a point where gravity is so dense that not even light can escape it.