Go to the companies web site and look for the rebate

Jonathan, the rebate is applied for directly on the manufacturer's website. They will have the instruction as to whether you can register online or mail in. As an example with Smith and Wesson : smithandwessonrebates.com/#/home

Are you referring to a firearm or ammo manufacturer's rebate? Most usually, they will require one to send in a completed rebate coupon and proof of purchase/sales receipts to the manufacturer. Most have instructions and coupons/rebate forms on their company web sites. Hope this helps!