The answer to 'how to kill spider' is to use a spider-killing spray or insecticide. Start by identifying the type of spider and then choose an appropriate insecticide specifically formulated to kill that species. Spray the insecticide directly on the spider or in areas where you've seen them, such as corners, crevices, and around windows and doors. Follow the product instructions carefully, including any safety precautions.
If you have a severe spider infestation or are dealing with venomous spiders, it's best to call a professional pest control technician. They have the expertise and equipment to safely and effectively eliminate spiders from your home.