Carbohydrates, one of the macronutrients, provides fuel for the central nervous system and energy for working muscles. Carbohydrates also regulate blood glucose and prevent protein from being used as an energy source and enable fat metabolism. Carbs are also important for brain function.
The difference between simple and complex carbs are their chemical structure and how fast sugar is absorbed and digested.
So as an example, when we eat candy, which is a simple carb and simple sugar, it is absorbed more quickly than complex carbs (example whole grain bread).
Problem often with simple carbs is, that they are processed and do not have any nutrition value meaning there are no vitamins, minerals or fiber in it.
But example fruit contains simple sugar but has nutrition value, but because of fibre, blood sugar levels are not spiking too high too quickly and also digestion will slow down.
Complex carbs are often referred to as starchy foods and they provide more sustained energy.
We should focus to get primarily complex carbs in our diet, including vegetable and whole grains.
Unrefined whole grains contain vitamins and minerals and are rich in fibre, which helps our digestive system work properly and it slows the release of insulin in the blood.
Common recommendation for carbohydrates are mainly 45-60% . For athletes and people who are very active the carb ratio increases because the body needs the fuel to replace glycogen stores quickly but I think if your activity level is very low it is more important to concentrate what type of carbs you are eating. Avoiding ketosis carbohydrate intake should be over 100g per day and healthy rating is above 30 to 40% of your daily calories depending also on your physical activity.