The first step is to get the cat to the vet and rule out any
underlying medical problem.

if the litter box is the type with a cover,  some cats dont like it and wont
use it, also if there is something in the house that makes him uncomfortale
like a dog or children, he may pee somewhere

cats naturally want to use a litter like product to bury their waste. (some
cats won't bury, and that is a dominance issue, but that is digressing)  I
have fostered kittens for years, and never have I had to 'teach' a cat to
use it.  It is a natural instinct.

If you have a cat who isn't using the box, there is a reason for it.    He
might not like the fact that the box is dirty.  It should be scooped daily -
do you want to walk over your day old poop to pee?  I don't think so!  You
don't mention if you have any additional pets.  If there is another cat,
make sure there are additional boxes.

Have you changed anything recently regarding the litter box?  Change in
litter, change in the type of box (covered / uncovered) might upset the cat
into not using it.  Also the box should be in a quiet area, and not one of
high traffic flow so the cat feels secure in using it.

If the cat is eating well, and acting normally other than the litter box,
the cheapest option would be to buy a second litter box and put it in a
different place, and see if that helps.  If it does, problem solved.  If it
doesn't, a vet visit is absolutely in order.  Peeing outside of the box is a
sign that the cat is uncomfortable using the box, and if that is medical,
then it could be that he has a urinary problem which COULD be fatal.

If the cat is not acting normally, or stops eating, then the cat needs to be
seen by a vet IMMEDIATELY (see the fatal part of the last paragraph)

I agree with the other replies but also wanted to add a little
something.  You might want to put the box back where it was,
because moving it does upset and sometimes confuse them,
especially when they are young.  More boxes is better, and
also....never keep a litter box near the cat food....
no one, especially not a fastidious cat, wants to
eat their lunch next to an outhouse.

--tension

cats don't like to do their business close to their food.

have you changed the type of litter?

is the tray cleaned on a regular basis?

if the cat has done his business in the wrong place, he will carry on using
that spot as long as the smell remains.  you should wash the area with a
solution of water and biological washing powder.  the bio powder breaks down
the enzymes and eliminates the smell.

as also suggested a visit to the vet would not do any harm.

when moving a tray move it gradually, ie a few feet away each time. each
time it is moved make an effort to show him where it is.