how to set discount for particular item?

That was really a spammer

@progreccor
You will need to create a discount and restrict it to one product category and then make sure that your products are into that category (you can have more that one category for a product so you can create a fake category and leave it unpublished just to be able to do that.
Restrictions on discounts and coupons are only available in our commercial editions.

@adeptdesigns
You could turn on the the auto load option of the coupon (commercial editions only) so that the coupon is loaded automatically.
However, the system won't exactly behave as you want. You can set a minimum number of products so that it's only loaded once that minimum is reached, and you can set the coupon to only be loaded if a product of a category is in the cart, but you won't be able to tell it to only be activated if four specific products are in the cart at the same time. That's too complex for the current system. More information on discounts and coupons can be found here:
www.hikashop.com/en/support/documentatio...p-discount-form.html