Seth was a son of Adam and Eve, being born when Adam was 130 years old (out of a 930 year lifespan). Seth was born after his brother Abel had been murdered by his eldest brother Cain. The name Seth probably means granted.
Although Adam and Eve had many other children, it was from the line of Seth that the Biblical story continues. Noah comes from the line of Seth (Genesis 5). The line of Jesus is likewise traced through Seth (Luke 3:38).
As with other humans during that time, Seth is recorded as having lived a long life, 912 years in all. (Gen 5:8)