There are lots of great books and articles on basic horse care, here is one example if you want to take a look: Basic Horse Care Information
Feeding: please feed your horse by weight according to the horse's age, amount worked, and during Winter if you live in a colder climate, please provide additional feed - that provides added warmth. Consider purchasing or borrowing a scale to weigh feed so the horse is getting what he needs according to his ideal weight, otherwise you may under- or over-feed without realizing it.
Horses do best when their diets and routines are not changed drastically. Any changes in feed ideally need to be made gradually. Horses are large and powerful but in many ways are fragile.
Please provide a salt/trace mineral block, and water 24/7, and I hope you have adequate shelter so the horse has the option of getting out of the elements.
Regular hoof trims.
These are some of the very basic basics.
As for learning how to work with your horse, if you have no prior experience, I suggest finding someone with experience who has a soft hand and a good manner with horses, it's best to learn by real watching and doing. If you don't have a person like that available to learn from, and are off of books, videos, and so forth, please be careful - some trainers are great marketers but unfortunately that's about it.