Carbohydrates, also called "glucids", are substances with a sweet taste, at least the most simple ones. there are three types of carbohydrates. The simplest are the 3 monosaccharides, glucose, fructose and galactose. Even though they have the same structure, these 3 carbohydrates can have very different properties for our organism. For example some enzymes are only active with glucose, not with fructose. Every time 2 monosaccharids join together, they produce a slightly more complex carbohydrate: the disaccharides:
Sucrose, which is the standard sugar which you find in your homw, is the disaccharide which is formed by the union of glucose and fructose. Lactose, the sugar found in milk and dairy products, is formed by the union of glucose with galactose, whilst maltose, the sugar derived from starch, is formed by the union of 2 molecoles of galactose.
When more than 2 monosaccharides join together, they form more complex carbohydrates, the polysaccharides. The most important polysaccharide in our diet is starch, which is found mainly in foods of veetable origin, such as pasta, bread, rice, pulses, bananas and chestnuts. As well as starch we have glycogen, found in meat and liver, and vegetable fibres, the substances which constitute the 'skeleton' of plants

Where do you find them?

Simple sugars:
honey, jam, dried fruit and nuts, table sugar and sweets in general.
Complex sugars:
Pulses, chestnuts, potatoes, cereals and cereals derivates
(bread, pasta, breadsticks etc)

As well as amid and proteins, pulses and wholemeal cereals contain a good % of fibres in the external skin that covers the seeds or the beans.