First you need to eliminate their reason for coming inside in the first place. That means cleaning the entire kitchen and putting all the food in containers or storage bins. The ants are coming in to get snacks, and as long as there is food available they will return because they have marked your kitchen down as the local spot to go. Cleaning will also remove the chemical markers their explorers lay down to guide the rest of the troops to the goodies. After you clean well, get a good household bug spray and find where it is they come in at. Spray the outside and inside around the entrance with the spray. You will need to continue keeping your foodstuffs in containers and the kitchen kept clean or they will still return eventually. You need to avoid leaving dirty dishes in the sink or letting the garbage can sit for more than a day before emptying it. Anytime you find even a lone ant, you need to clean well because it left a chemical trail for the others to follow. Mostly, it's just a matter of keeping the food put away and unavailable, and cleaning well, to discourage the ants from visiting in numbers.