Can anyone please inform me how infection occur? or how does it develop? or its etiology?

any infection...Can anyone please inform me how infection occur? or how does it develop? or its etiology?
Check out this link for how your immune system works:
http://www.immunealert.com/science3.asp...
it is cause by shaking hands near persons when they r have cold,or drinking water contained by the glass surrounded by which other people enjoy drank,by scratching wounds,by getting that injection which be injected to somebody else and there r plentiful more reasons of it.
An infection occur when a virus of bacteria invades the body former the peripheral (innate) immune system. A adjectives case is when the epidermis (skin) cell are penetrated or through the passage of mucus membranes (nostrils/breathing). Usually following is the inflammation of the infected nouns due to the increase of blood flow to the area so that leukocytes such as white blood cell can "kill" off these cell. One infected cell dies and the infecting agent (antigen) moves on to penetrate other cellular membranes and so on, until it is removed. Usually most antigens withdrawal the ability to live outside of a cell due to a want of certain conditions, surrounded by this case if interferons pervent the antigen from entering cell, it will die off surrounded by the extracellular fluid.