Koi take care of themselves for the most part, but it is up to you to keep their pond clean and to provide the with adequate nourishment. The amount of cleaning you do is dependant on how good your filter system is. An efficient filter system will require minimal maintenance whereas a cheap and poorly designed system will require a ton of work to keep it running.
Koi are usually fed twice a day. Only give them an amount of food that they can eat within 5 minutes. They may spend most of their day begging for good, but don’t overfeed, since it can lead to poor water quality and obesity problems. Koi have different feeding requirements for each season.