Every garage door threshold we sell comes with printed instructions on how to install it. That said, a lot of our customers want to know how difficult it is to install the garage door threshold and if it will seal their garage door. Installing a garage door threshold is simple & it will absolutely seal the garage door as long as the seal on the bottom of the door is still good. The threshold works in conjunction with the door bottom seal to keep water, dirt, debris, insects and rodents out of your home!