Dorissim, the problem with nutrition is that there are so many different points of view out there. And actually humans are amazingly adaptable about their diet at least in the short term (probably due to our hunter-gatherer ancestors) and the question is whether there is an optimum to minimise longterm health problems.
I think the key is probably "moderation in all things". We need some protein, some carbohydrate, some fat and some fibre, but too much of any of those might not work out well eventually.
Carbohydrate, as people say above, is our main energy food. However it is best to eat carbohydrates that are absorbed slowly, if they are absorbed quickly they produce a spike in the blood glucose concentration which is the risk factor mentioned for eventual insulin issues (diabetes). The fastest absorbed carbohydrate is the simple sugar found in sweets or cakes, so those are definitely things to have in moderation. Interestingly although the same simple sugars are found naturally in fruits, because they eaten in combination with so much fibre they are absorbed more slowly. Even relatively slight processing of the fruit, for example turning it into a juice which still contains fibre, speeds up the absorption.
The same is true for more complex carbohydrates, for example the starch found in wheat. Those carbohydrates are absorbed more slowly than simple sugars because they need to be broken down first. However after the wheat has been milled to make flour, purified to make the flour white, and then processed to make bread or pasta, the speed of absorption is faster. You are better off taking some of your carbohydrate as wholewheat bread or pasta, and brown rice, and carbohydrate-containing vegetables cooked simply.
Personally I think the most important nutritional advice is actually "don't snack". It is much better for your insulin levels and risk of diabetes if after eating a meal you let it all get absorbed and turned into energy, including the carbohydrate that goes into short term storage to keep producing energy after insulin levels have fallen. If a couple of hours after your last meal there is more food in your stomach your body will use that preferentially, keeping the insulin levels raised and encouraging the extra calories to be stored as fat (long term store).