The main function of a disaccharide is to be a quick source of energy.
Because they're only made of two sugar molecules, it's quick and easy for enzymes in your digestive system to break them down into monomers, absorbing them into your bloodstream.
We see disaccharides in our everyday life.
Sucrose is normal table sugar! It's likely the thing you add to your cup of tea!
Lactose is found in milk and dairy products. Many people are lactose intolerance, this means they lack the enzyme lactase so their digestive system isn't able to hydrolyse lactose to galactose and glucose.
But... do you remember what a disaccharide monomer unit is called?