I would like to know what a controller of an outboard motor is. Is it a
part of the steering mechanism? Does it usually come with a boat? Or do
I need to buy it separately? Is it a costly item relative to the total
cost of an outboard motor?

The reason why I am asking this is that I am looking for a used
outboard motor. eBay has some outboard motors. But some of them are
missing controller. I have no idea what's the significance of missing a
controller.

Thanks in advance for any info.

Jay Chan