Answer:
Primarily, they make pesticides, herbicides, and, oddly enough, the seeds for many foods we eat, some of which are genetically engineered. Their primary consumer is obviously farmers, so, while a food you eat wasn't PRODUCED by Mansanto, it was technically MADE by Mansanto.
They've received a lot of bad press over the genetic engineering, but that's a matter of principle and beliefs than scientific proof.
Hope this helps. :)