If you are having trouble getting your cat to use the litter box, several issues may be at influence. A check at the vet is a good idea for a start, in case your kitty is having a medical issue like bladder stones that make urination painful. After a medical check, you might try using a product like this one to get kitty on board with litter box use.
Dr. Elsey's Ultra Litter Attractant is a natural and biodegradeable product designed to prevent litter box aversion. It can be used in clumping litter as a natural attractant to cats.
Owners who have successfully used this product have made other changes to their kitty's environment to encourage proper litter box use, including moving the box to a new, more preferable (to kitty) location, and changing the style of box (from covered to uncovered, for instance) along with using different types of litter.
