What are the uses of combine harvesters?

Farmers.

To gather crops that are either still standing or have been cut into a swath, separate the seeds from the leaves and stems (called chaff), and store the seeds in a holding bin at the top of the...

They are those huge machines that you may have seen working in feilds, they basically harvest mass quantities of weat, or something else.

using a combine is the easiest way to harvest oats, yes

It was invented in the U.S. in 1834 by Hiram Moore. It was pulled by a team of horses, and the running gear was driven off of the wheels. So if it was muddy, the wheels slipped and the combine...