In ancient times, people lived by eating the meat of hunted birds and animals. Shennong had a large population when he lived, and there were not enough birds and animals for people to hunt and eat. At this time, Shennong made farm tools and taught people to farm according to the climate and land conditions.
The key point here is "when Shennong died in Heaven".
To: to
Yes: at this moment, here it is.
"reason": by virtue of, based on