Final answer:
The first elements formed in stars were hydrogen, helium, and lithium, with heavier elements being created later within the stars themselves.
Step-by-step explanation:
The three elements that were among the first formed in stars are hydrogen, helium, and a small amount of lithium. These lightest elements were produced in appreciable abundances during the early stages of the universe when it was hot enough for fusion to occur. All heavier elements were formed later within the interiors of stars. Over time, stars engaged in nucleosynthesis, creating heavier elements and ejecting them into space, enriching the interstellar medium and future generations of stars.