A disease is any condition in which the body is not working properly. Many diseases are quite trivial and clear up quickly without treatment, for example a cold. Some are severe, even life-threatening, such as many, not all, types of cancer.
Infections are one particular type of disease. An infection is a disease caused by a living organism (a germ), which is living in the body of the affected person. The germ may be a bacterium, virus, fungus or parasite.
Like all diseases, infections vary in how severe they and whether they need treatment. The common cold is a virus infection; colds are not dangerous unless a person is already sick or very weak. Tuberculosis is a bacterial infection, which can be very difficult to treat and causes many deaths every year.