Calories in vs. calories out basically refers to the idea that as long as you consume less calories than what you burn (or an equal amount), you will be successful in losing weight. This is a very simplified way of looking at dieting and weight loss, and while it may work for some people, there are a lot more things you should understand about healthy eating and exercise before you give it a try.
Weight loss actually requires a calories deficit, meaning that you will need to consume fewer calories than what you are burning in order to see a result. However, if you aren’t giving your body the right nutrients and strength to exercise these calories off, you may find it difficult to get moving. If you are wanting to try this kind of approach it would be helpful to do some research into what you need for a balanced and active diet, to ensure you’re not going to lose energy and burn out quickly. Keep in mind that different foods can do different things to your body, so while you may consume the same amount of calories of two different things, one of them may make you feel fuller than the other.