Does anybody know a great way to get a flat stomach?

I don’t have a huge stomach or nothing really flabby but I know that if I don’t start something that’s how it will end up. I really don’t want to spend any money on equipment unless I have to. So could you help me please with something that’s helped you. I love to work out so if you have a remedy that way I’d love to hear it as well. Thanks in advance! :)